Neuroanatomy and Neuroembryology

I. Terminology

A. Anatomical references

1. Anatomical structures can be divided into front and back

a. Front

i. Anterior

ii. Rostral

            b. Back

                        i. Posterior

                        ii. Caudal

2. Anatomical structures can be divided into top and bottom

            a. Superior

                        i. Dorsal (Posterior for bipeds)

            b. Inferior

                        i. Ventral (Anterior for bipeds)

3. Anatomical structures can be divided into sides

            a. Midline

            b. Medial

                        i. Close to the midline

            c. Lateral

                        i. Away from the midline

4. Relative position of anatomical structures

            a. Ipsilateral

                        i. Structures localized to the same side

            b. Contralateral

                        i. Structures localized to different sides

            c. Proximal

                        i. Close to a fixed reference point

            d. Distal

                        i. Distant to a fixed reference point

5. Anatomical structures can be sectioned along flat surfaces (planes)

            a. Coronal (frontal)

                        i. Vertical plane dividing structure into anterior/posterior parts

            b. Sagittal

                        i. Vertical plane dividing structure into right and left halves

                        ii. Midsaggital (median)

                        iii. Parasagittal

            c. Horizontal (transverse)

                        i. Divides structure into superior and inferior

6. Longitudinal axis

            a. Nervous system is organized along an anterior to posterior axis

            b. Different regions of the brain have different longitudinal axis

i. Cerebellum is ventral to the forebrain axis but dorsal to that of the brain stem

 

Note: The nervous system is organized along an anterior to posterior axis with a fluid filled tube running through the center. At the anterior end, the structure have enlarged with evolutionary advancement and to accommodate for this enlargement, the brain has become distorted and curved so that some structures are more difficult to assign anatomical references.

 

B. Nervous system terminology

1. Neural cell bodies are often organized in rows

            a. Lamina

i. Row or layer of cell bodies separated from another row or layer by a layer of axons or dendrites

ii. Parallel to structural surface

            b. Column

i. Row of cells perpendicular to the surface of the brain

ii. Share a common function

2. Terms referring to neuron cell bodies found in CNS

            a.  Grey matter

i. Generic term for neurons in the CNS

            b. Nucleus

i. Clearly defined mass of neuron cell bodies

            c. Substantia

i. Less distinct borders than nuclei

            d. Locus

i. Small but well defined mass of neuron cell bodies

3. Terms referring to neuron cell bodies found in PNS

            a. Ganglion

i. Collection of neurons in the PNS

4. Terms referring to axons

            a. White matter

i. Generic term for a collection of axons

            b. Tract (projection)

i. Refers to CNS

ii. Set of axons, also known as fibers, that project from one structure and form synapses on a second common structure

            c. Nerve

i. Refers to PNS

ii. Bundle of axons either projecting from the CNS to a muscle or gland or from a sense organ to the CNS

            d. Bundle

i. Collection of axons that run together but do not necessarily share the same origin or destination

            e. Commissure

i. Any collection of axons that connect one side of the brain with the other side

5. Terms that refer to the external morphology of the brain

            a. Surface convolutions

                        i. Gyrus: ridge on the surface of the cerebrum (and cerebellum)

                        ii. Sulcus: groove

                        iii. Fissure: a deep groove

6. Important sulci and gyri

            a. Central sulcus

i. Separates frontal (anterior) and parietal lobes (posterior)

            b. Precentral gyrus

i. Commonly known as the motor cortex

            c. Postcentral gyrus

i. Somatosensory cortex

            d. Sylvian (lateral) fissure

i. Separates temporal and frontal lobes

ii. Temporal is inferior to the frontal and extends to the caudally located occipital lobe

iii. Parietal lobe is superior to lateral fissure

            e. Insula

                        i. Fold created by the temporal lobe

ii. Commonly referred to as the operculum

f. Parieto-occipital sulcus

i. Extends from superior to inferior surface

ii. Divides parietal from occipital lobes

            g. Calcarine sulcus

i. Medial surface of the occipital lobe

ii. Defines the location of the visual cortex

            h. Cingulate sulcus

i. Medial surface of the frontal and parietal lobes

ii. Inferior to this sulcus is the limbic lobe

 

C. Organization of the nervous system

1. Functionally organized into two divisions

            a. Central nervous system (CNS)

                        i. Brain (Cerebellum, cerebrum and brain stem)

                        ii. Spinal cord

            b. Peripheral nervous system (PNS)

                        i. Somatic

                        ii. Autonomic

2. Organization of gray and white matter

            a. CNS

                        i. Gray matter is organized on the surface of the brain in lamina

ii. White matter is organized centrally

iii. White matter constitutes the majority of brain mass

            b. PNS

                        i. Gray matter is centrally located

                        ii. White matter is organized on the surface

 

II. Cerebral Hemispheres

A. General characteristic of the cerebral hemispheres

1. Organized into functional areas

            a. Motor

                        i. Voluntary control of movement

            b. Sensory

                        i. Conscious awareness of sensation

            c. Association

                        i. Integration

                        ii. Emergent properties

2. Contralateral control of the body

            a. Each hemisphere is concerned with the opposite of the body

3. Functions are lateralized

            a. Each hemisphere has unique functions

4. Function arises from concerted activity

5. Lobes

            a. Frontal

            b. Parietal

            c. Temporal

            d. Occipital

B. Motor areas

1. Cortical areas involved in movement

            a. Primary motor cortex

            b. Premotor cortex

            c. Broca’s area

            d. Frontal eye field

2. Primary motor cortex (Brodmann 4)

            a. Located in the precentral gyrus of frontal lobe

            b. Conscious control of motor execution

            c. Pyramidal cells give rise to the corticospinal tracts

            d. Somatotopy

                        i. Body is mapped (motor homunculus)

                        ii. Representation is proportionate to level of motor control

                        iii. Innervation is primarily contralateral

3. Premotor cortex (Brodmann 6)

            a. Learned motor skills

                        i. Patterned or repetitious

4. Broca’s area (Brodmann 44/45)

            a. Directs muscles of the tongue, throat and lips

            b. Motor planning for speech related activity

5. Frontal eye field (Brodmann 8)

            a. Voluntary movement of the eyes

C. Sensory areas

1. Cortical areas involved in processing sensation

            a. Primary somatosensory cortex

            b. Somatosensory association area

            c. Visual cortex

            d. Auditory cortex

            e. Olfactory cortex

            f. Gustatory cortex

2. Primary somatosensory cortex (Brodmann 1, 2 & 3)

            a.  Parietal lobe

                        i. Postcentral gyrus

            b. Somatic senses

                        i. Pain and temperature

                        ii. Touch and proprioception

            c. Somatotopy

                        i. Body is mapped (somatosensory homunculus)

                        ii. Representation is proportionate to number of sensory receptors

                        iii. Innervation is primarily contralateral

3. Somatosensory association area (Brodmann 5 & 7)

            a. Integrate various somatic sensory inputs

4. Visual areas

            a. Primary visual cortex (Brodmann 17)

i. Occipital lobe

                        ii. Located primarily in the calcarine sulcus

                        iii. Sensory function with largest cortical representation

                        iv. Innervation is primarily contralateral

            b. Visual association areas (Brodmann 18 & 19)

                        i. Interpretation of visual stimuli

                        ii. Past visual experiences

5. Auditory areas

            a. Primary auditory cortices (Brodmann 41)

                        i. Superior margin of temporal lobe

                        ii. Pitch, rhythm and loudness

            b. Auditory association area (Brodmann 42 & 43)

                        i. Recognition of stimuli as specific auditory experiences (e.g., speech)

6. Olfactory cortex

            a. Medial aspects of temporal lobe

                        i. Piriform lobe (uncus)

7. Gustatory cortex (Brodmann 43)

            a. Parietal lobe deep to the temporal lobe

 

D. Association areas

1. Characteristics

a. Analyze, recognize and act on sensory in puts

b. Multiple inputs and outputs

2. Association areas (in addition to those discussed above)

            a. Prefrontal cortex

            b. Gnostic area

            c. Language areas

3. Prefrontal cortex (Brodmann 11 & 47)

            a. Anterior portion of frontal lobe

            b. Intelligence, complex learned behavior and personality

            c. Understanding written and spoke language

4. General interpretation area

            a. Encompasses parts of temporal, parietal and occipital lobes

                        i. Generally found on the left side

            b. Storage of complex sensory memories

5. Language areas

            a. Bilaterally located

            b. Wernicke’s area

                        i. Posterior temporal lobe on left side

                        ii. Sounding out unfamiliar words

            c. Affective language areas

                        i. Located contralateral to Broca’s and Wernicke’s areas

                        ii. Nonverbal and emotional components of language

E. Organization of the cortex

1. Common features

            a. Cell bodies are arranged in sheets (layers)

                        i. Parallel to surface of brain

            b. Layer I lacks cell bodies

                        i. Molecular layer

            c. At least one layer has pyramidal cells

                        i. Emit large apical dendrites

                        ii. Extend up to layer I

2. Cytoarchitecture

            a. Lamina

                        i. Layers of cells parallel to brain surface

            b. Columns

                        i. Row of cells perpendicular to brain surface

                        ii. Share a common function

3. Neocortical layers

            a. Layer I

i. Few cells; primarily axons, dendrites and synapses

            b. Layers II & III

i. Pyramidal cells that project to and receive projections from other cortical regions

            c. Layer IV

i. Stellate cells that receive most of thalamic input and project locally to other lamina

            d. Layer V & VI

i. Pyramidal neurons that project to subcortical regions such as the thalamus, brainstem, and spinal cord, and other cortical areas

 

III. Subcortical Structures

A. Basal nuclei (ganglia)

 

1. Structures

            a. Caudate

            b. Putamen

            c. Globus pallidus

2. Organization

            a. Receive inputs from most cortical structures

            b. Project to motor cortex via the thalamus

3. Function

            a. Motor control

                        i. Starting, stopping and monitoring movement

                        ii. Inhibit unnecessary movement

B. Diencephalon

1. Organization

            a. Core of forebrain

                        i. Surrounded by cerebral hemispheres

            b. Three bilateral structures

                        i. Thalamus

                        ii. Hypothalamus

                        iii. Epithalamus

2. Thalamus

            a. Comprised of multiple nuclei

                        i. Each nucleus receives specific afferent projections

                        ii. Nuclei interconnect

                        iii. Nuclei project (relay) processed information to particular cortical areas

            b. Process and relay information

3. Hypothalamus

            a. Location

                        i. Between optic chiasm and mammillary bodies

                        ii. Below thalamus

            b. Connected to the pituitary

                        i. Via infundibulum

            c. Visceral control center of the body

                        i. Autonomic control (e.g., BP, HR)

                        ii. Emotional response (e.g., fear, sex drive)

                        iii. Regulation of body temperature

                        iv. Regulation of feeding

                        v. Regulation of thirst

                        vi. Regulation of circadian rhythm

                        vii. Control of endocrine function

4. Epithalamus

            a. Pineal body

                        i. Control of sleep-cycle

                        ii. Melatonin

            b. Choroid plexus

                        i. Production of cerebral spinal fluid (CSF)

 

IV. Brain Stem

A. Organization

1. Functional areas

            a. Midbrain

            b. Pons

            c. Medulla oblongata

B. Functions

1. Autonomic behavior

2. Pathway for fiber tracts

3. Cranial nerves

C. Midbrain

1. Structures

            a. Cerebral peduncles

                        i. Fiber tracts connecting cerebrum with inferior structures

            b. Corpora quadrigemina

                        i. Superior and inferior colliculi

            c. Substantia nigra

                        i. Color is due to melanin (DA precursor)

                        ii. Nucleus of DA neurons

            d. Red nucleus

                        i. Motor reflex

            e. Reticular formation

                        i. Some of the RF nuclei are found here (see below)

D. Pons

1. Lies between midbrain and medulla

2. Comprised mostly of conducting fibers

            a. Connection between higher brain areas and spinal cord

                        i. Longitudinal projections

            b. Pontine nuclei

                        i. Relay information between motor cortex and cerebellum

3. Nuclei for several cranial nerves

            a. Trigeminal (V)

            b. Abducens (VI)

            c. Facial (VII)

E. Medulla oblongata

1. Lies between pons and spinal cord

            a. No obvious demarcation between medulla and spinal cord

2. Landmarks

            a. Pyramids

                        i. Descending corticospinal tracts

                        ii. Decussate

3. Nuclei for several cranial nerves

            a. Hypoglossal (XII)

            b. Glossopharyngeal (IX)

            c. Vagus (X)

            d. Accessory (XI)

            e. Vestibulocochlear (VIII)

4. Control of visceral motor function

            a. Cardiovascular center

                        i. Cardiac center

                        ii. Vasomotor center

            b. Respiratory center

                        i. Control rate and depth of breathing

            c. Reflex

                        i. Vomit

                        ii. Hiccup

                        iii. Swallowing

                        iv. Coughing

                        v. Sneezing

 

V. Cerebellum

A. Anatomy

1. Location

            a. Dorsal to pons and medulla

            b. Caudal to occipital lobe

2. Structure

            a. Bilateral

            b. Consists of cerebellar hemispheres

                        i. Connected by vermis

            c. Hemispheres consists of lobes

                        i. Posterior

                        ii. Anterior

                        iii. Flocolonodular

            d. Gray and white matter is organized like cerebrum

                        i. Gray outside/white inside

            e. Cerebellum is connected via cerebellar peduncles

                        i. Fiber tracts connecting brain stem and sensory cortices with cerebellum

B. Function

1. Precise timing of skeletal contraction

            a. Sensory and motor information is integrated

VI. Brain Systems

A. Limbic system

1. Group of cortical structures

            a. Located on medial aspect of the cerebral hemisphere and diencephalon

            b. Connectivity is complex

2. Structures

            a. Upper part of brainstem

            b. Rhinencephalon

                        i. Septal nuclei

                        ii. Cingulate gyrus

                        iii. Parahippocampal gyrus

                        iv. Hippocampus

            c. Amygdala

            d. Diencephalon structures

                        i. Hypothalamus

                        ii. Anterior nucleus of the thalamus

            e. Fiber tracts

                        i. Fornix

                        ii. Fimbria

3. Function

            a. Emotional and affective state

B. Reticular formation

1. Complex of nuclei and white matter

            a. Disperse and widespread connectivity

2. Location

            a. Central core of medulla, pons and midbrain

3. Function

            a. Maintain wakefulness and attention

                        i. Coordination of all afferent sensory information

            b. Coordination of muscle activity

                        i. Modulation of efferent motor information

 

VII. Protection of the Brain

A. Primary mechanism

1. Bone

            a. Brain is encased in a bony skullcap

2. Membranes

            a. Meninges

3. Fluid

            a. Cerebrospinal fluid

            b. Blood-brain barrier

B. Meninges

1. Structure

            a. Three connective tissue membranes

                        i. Dura mater (tough mother)

                        ii. Arachnoid mater (spider mother)

                        iii. Pia mater (gentle mother)

2. Dura

            a. Two fused layers

                        i. Periosteal layer

                        ii. Meningeal layer

            b. Periosteal layer is attached to the skull

                        i. Spinal cord does not have a periosteal layer

            c. Meningeal layer covers brain and spinal cord

            d. Dura projects inward to help anchor the brain

            e. Dural septa

                        i. Falx cerebri

                        ii. Falx cerebelli

                        iii. Tentorium

            f. Dural sinuses

                        i. Spaces between dural layers

                        ii. Collect venous blood flow from brain

                        iii. Directs blood flow back to jugular veins

3. Arachnoid

            a. Loose cover over brain

                        i. Does not enter sulci

            b. Small space between dura and arachnoid

                        i. Subdural space

            c. Subarchnoid space

                        i. Deep to arachnoid

                        ii. Filled with CSF

                        iii. Secured to pia by weblike extensions of the arachnoid

            d. Arachnoid villi

                        a. Act like valves

                        b. Projection of archoid through dura into dural sinuses

                        c. Permits CSF to be absorbed into venous blood

4. Pia

            a. Clings tightly to brain

            b. Invested with blood vessels

 

C. Cerebrospinal fluid (CSF)

1. Function

            a. Form a liquid cushion for CNS organs

            b. Provides nutrients

            c. CSF composition is monitored

                        i. Control of autonomic functions

2. Found in ventricles (see below) and central canal of spinal cord

3. Choroid plexuses

            a. Produce CSF

            b. Located in ventricles

4. Flow

            a. Produced in ventricles

            b. Exit 4th ventricle

            c. Bath brain

            d. Absorbed into venous blood through arachnoid villi

5. Anatomy of the ventricular system

            a. Four fluid-filled chambers

                        i. Paired lateral

                        ii. Third

                        iii. Fourth

b. Chambers are continuous with each other and with the central canal of the spinal cord

c. Interventricular foramen connect lateral with third

d. Third is connected with fourth via cerebral aqueduct

e. Fourth is continuous with central canal

f. Fourth has openings to subarachnoid space

            i. Lateral apertures

            ii. Median aperture

 

 

D. Blood-brain barrier

1. Brain environment is tightly controlled

            a. Most bloodborne substances cannot readily enter the brain

2. Mechanism

            a. Capillary endothelium is joined by tight junctions

                        i. Relatively impermeable

3. Barrier is selective

            a. Facilitated diffusion of particular substances

                        i. Glucose and others

            b. Cannot prevent fat-soluble molecules from diffuses into brain

 

VIII. Spinal Cord

A. Gross anatomy

1. Protected

            a. Bone

                        i. Vertebral column

            b. Membranes

                        i. Meninges

            c. Fluid

                        i. CSF

2. Meninges

            a. Single layer

                        i. Spinal dural sheath

            b. Epidural space

                        i. Padding of fat between vertebrae and dural sheath

            c. Subarachnoid space

                        i. Filled with CSF

            d. Extend to S2

                        i. Spinal cord only extends to L1

3. Attachments

            a. Denticulate ligaments

                        i. Attached to vertebrae laterally

            b. Filum terminale

                        i. Attached to coccyx caudally

B. Cross-sectional anatomy

1. Meninges

            a. Dura

            b. Arachnoid

            c. Pia

2. Gray matter and spinal roots

            a. Gray is organized like a butterfly

                        i. Bridge—gray commissure

            b. Gray matter columns

                        i. Posterior (dorsal) horn

                        ii. Anterior (ventral) horn

                        iii. Lateral horn (thoracic and superior lumbar regions only)

3. Anterior horn

            a. Cell bodies of somatic motor neurons

            b. Send axons via ventral root

4. Lateral horn

            a. Cell bodies for autonomic motor neurons

                        i. Sympathetic NS

            b. Leave via ventral root

5. Dorsal root ganglion

            a. Cell bodies of sensory neurons

            b. Axons project to cord via dorsal root

                        i. Some enter white matter tracks and ascend

                        ii. Some synapse with interneuron located in posterior horn

6. Spinal nerves

            a. Lateral fusion of ventral and dorsal roots

            b. Part of PNS (see below)

C. Spinal pathways

1. Characteristics

            a. Most pathways decussate

            b. Most are poly-synaptic

                        i. Two or three neurons

            c. Most are mapped

                        i. Position in cord reflects location on body

            d. All pathways are paired

2. Ascending (sensory) pathways (see sensory systems)

            a. Dorsal column (fasciculi cuneatus and gracilis)

                        i. Touch and proprioception

            b. Spinothalamic (anterior and lateral)

                        i. Pain and temperature

3. Descending (motor) pathways (see motor lecture)

            a. Upper motor neurons

                        i. Cell bodies in brain

            b. Lower motor neurons

                        i. Cell bodies in anterior horn of spinal cord

            c. Direct

                        i. Anterior and lateral (pyramidal) corticospinal tracts

            d. Indirect (tracts)—multi-neuronal

                        i. Rubrospinal

                        ii. Vestibulospinal

                        iii. Reticulospinal

                        iv. Tectospinal

 

IX. General Organization of the Peripheral Nervous System

A. Background

1. Function

            a. Connect brain with outside world

                        i. CNS function is dependent on information

2. Structural components

            a. Sensory receptors

            b. Peripheral nerves and ganglia

            c. Efferent motor endings

B. Sensory receptors

1. Nature of stimulus detected

            a. Mechanoreceptors

                        i. Touch, vibration, pressure, stretch

            b. Thermoreceptors

                        i. Temperature changes

            c. Photoreceptors

                        i. Light energy

                        ii. Exclusively in the retina

            d. Chemoreceptors

                        i. Chemical in solution

            e. Nociceptors

                        i. Pain

2. Location

            a. Exteroceptors

                        i. Surface of skin

            b. Interoceptors

                        i. Visceroceptors

                        ii. Visceral organs and blood vessels

            c. Proprioceptors

                        i. Musculoskeletal organs

3. Complexity

            a. Simple

                        i. Most sensory receptors (generalized)

            b. Complex

                        i. Special senses (vision, audition, olfaction, gustation)

4. Generalized sensory receptors

            a. Free dendritic endings (unencapsulated)

                        i. Free

                        ii. Merkel discs

                        iii. Root hair plexus

            b. Encapsulated

                        i. Meisner’s corpuscles—low frequency vibration)

                        ii. Pacinian corpuscles—high frequency

                        iii. Ruffini’s corpuscles—deep pressure

                        iv. Muscle spindles—muscle stretch

                        v. Golgi tendon organs—tendon stretch

 

C. Nerves

1. Parallel bundles of peripheral axons

            a. Enclosed by connective tissue

            b. Some may be myelinated

2. Classification based on nature of information

            a. Sensory (afferent) nerves

                        i. Sensory information from periphery to CNS

            b. Motor (efferent) nerves

                        i. Motor information from CNS to periphery

            c. Mixed nerves

                        i. Include sensory and motor

3. Classification based on site of origin

            a. Cranial nerves

                        i. Brain origin

            b. Spinal nerves

                        i. Arise from spinal cord

 

D. Motor endings

1. Function

            a. Activate effectors

                        i. Release of neurotransmitter

2. Types

            a. Neuromuscular junction

                        i. Contact between motor neuron and muscle

                        ii. Release ACh

            b. Varicosities

i. Contact between autonomic motor endings and visceral effectors and organs, smooth and cardiac muscle

 

E. Cranial nerves

 

 

Cranial Nerve

Sensory Function

Motor Function

I

Olfactory

YES—smell

NO

II

Optic

YES—vision

NO

III

Oculomotor

NO

YES—eye muscles

IV

Trochlear

NO

YES—eye muscle

V

Trigeminal

YES—general sensation

YES—chewing

VI

Abducens

NO

YES—abducts eye

VII

Facial

YES—taste

YES—facial expression

VIII

Vestibulocochlear

YES—audition; balance

NO

IX

Glossopharyngeal

YES—taste

YES—tongue and pharynx

X

Vagus

YES—taste

YES—pharynx and larynx

XI

Accessory

NO

YES—head and neck movement

XII

Hypoglossal

NO

YES—tongue

 

X. Spinal Nerves

A. Nomenclature

1. Named for the level of the vertebral column from which the nerves exits

            a. 31 spinal nerves

                        i. 8 cervical (C1 – C8)

                        ii. 12 Thoracic (T1 – T8)

                        iii. 5 Lumbar (L1 – L8)

                        iv 5 Sacral (S1 – S8)

                        v. 1 Coccygeal (C0)

B. Structure (see above)

1. Dorsal and ventral rootlets

2. Dorsal and ventral root

3. Dorsal root ganglion

4. Spinal nerve

5. Dorsal ramus of spinal nerve

6. Ventral ramus of spinal nerve

7. Rami communicantes

            a. Autonomic fibers

8. Sympathetic chain ganglion

B. Nerves plexuses

1. Specific to ventral rami

2. Types

a. Cervical

b. Brachial

c. Lumbar

d. Sacral regions

3. Fibers of different ventral rami cross and are redistributed

            a. Branches contain fibers originating from different spinal nerves

            b. Innervation arrives via multiple routes

                        i. More than a single spinal nerve serves each limb muscle

 

C. Dermatomes

1. Area of skin innervated by the cutaneous branch of a single spinal nerve

2. All spinal nerves (except C1) have dermatomes

3. Dermatomes overlap

 

XI. Reflex Activity

A. Background

1. Stimulus-response sequence

            a. Unlearned

            b. Unpremeditated

            c. Involuntary

2. Mediated by spinal cord circuits

            a. Information may ultimately relayed to the brain

B. Components of a reflex arc

1. Receptor

            a. Site of stimulus action

2. Sensory neuron

            a. Transmits the afferent impulse to the CNS

3. Integration center

            a. Monosynaptic reflex

                        i. Single synapse

            b. Polysynaptic

                        i. Multiple synapses with chains of interneurons

4. Motor neuron

            a. Conducts efferent impulse from integration center to effector

5. Effector

            a. Muscle fiber or gland

C. Stretch and deep tendon reflexes

1. Muscle spindles

            a. Consist of intrafusal fibers

            b. Wrapped by afferent sensory endings

                        i. Type Ia fibers

                        ii. Type II fibers

            c. Gamma (g) efferent fibers

                        i. Innervate contractile region of spindle

                        ii. Maintain spindle sensitivity

2. Extrafusal muscle fibers

            a. Skeletal muscle

            b. Innervated by alpha (a) motor neurons

3. Sequence of events

            a. Stretching muscle activates muscle spindle

            b. Impulse carried by primary sensory fiber to spinal cord

            c. Activates alpha motor neuron

                        i. Sends efferent signal to muscle (effect)

            d. Stretched muscle contracts

            e. Antagonist muscle is reciprocally inhibited

 

XII. Overview of the Autonomic Nervous System

A. Somatic Nervous System

1. Voluntary

a. Voluntary muscle movement

2. Sensory information to the CNS

3. Organization of cell bodies

a. Lie within spinal cord or brainstem

b. Targets are controlled monosynaptically

B. Autonomic Nervous System

1. Involuntary

a. Autonomic functions are carried out without conscious, voluntary control

2. Cell bodies of all lower autonomic motor neurons lie outside the CNS

a. Autonomic ganglia

b. Neurons are postganglionic

c. Driven by preganglionic neurons whose cell bodies are in the spinal cord or brainstem

3. Divisions

            a. Sympathetic

b. Parasympathetic

4. Divisions differ based on:

            a. Neurotransmitter type

            b. Fiber length

            c. Location of ganglia

            d. Function

5. Neurotransmitter

Division

Preganglionic

Postganglionic

Sympathetic

ACh

NE

Parasympathetic

ACh

ACh

           

a. ACh acts locally

            i. ACh always has a stimulatory effect

b. NE has spreads far and can exert its effects over long distances when circulated in the blood

c. Adrenergic receptors

            i. Alpha—stimulatory

            ii. Beta—inhibitory (except in the heart when it is excitatory)

6. Fiber length

            a. Parasympathetic

                        i. Long preganglionic

                        ii. Short postganglionic

            b. Sympathetic

                        i. Short preganglionic

                        ii. Long postganglionic

7. Location of ganglion

            a. Parasympathetic

                        i. Ganglion is located in visceral organ

            b. Sympathetic

                        i. Ganglia lie close to spinal cord

                        ii. Sympathetic chain ganglia

8. Function

            a. Divisions work in concert

            b. Parasympathetic dision

                        i. Maintenance of function

                        ii. Energy conservation

            c. Sympathetic division

                        i. Emergence

                        ii. Intense muscular activity

9. Sympathetic response

a. Pupil dilated

b. Secretory responses inhibited

c. Stimulates sweating

d. Heart function

i. Increases rate

ii. Dilates coronary vessels

e. Increased blood pressure

            i. Constricts most vessels

f. Bronchioles dilate

g. Decreased activity of digestive system

h. Piloerection

i. Increase metabolic rate

            i. Glucose is released into blood

            ii. Lipolysis

j. Increased alertness

            h. Causes ejaculation (vaginal reverse peristalsis)

10. Parasympathetic response

            a. Pupils constrict

            b. Stimulates secretory activity

                        i. Salivation

            c. Heart function

                        i. Decreases rate

                        ii. Constricts coronary vessels

            d. Constricts bronchioles

            e. Increases activity of digestive system

            f. Causes erection (penis and clitoris)

                        i. Vasodilation

 

XIII. Embryonic Development

A. Background

1. Brain development begins during third gestational week

            a. Ectoderm differentiates to form the neural plate

2. Neural plate invaginates to form the neural groove

            a. Groove deepens

            b. Folds fuse to form the neural tube

                        i. Occurs by the fourth week of gestation

3. Neural tube differentiates into the CNS

            a. Anterior portion forms the brain

            b. Posterior portion forms the spinal cord

4. Neural crest is formed when fold cells migrate laterally

            a. Neural crest gives rise to sensory neurons and autonomic neurons

5. Anterior develop is rapid

            a. Functional divisions are established

                        i. Primary brain vesicles

6. Types of primary vesicles

            a. Prosencephalon

                        i. Forebrain

            b. Mesencephalon

                        i. Midbrain

            c. Rhombencephalon

                        i. Hindbrain

7. Secondary vesicles form

            a. Forebrain is divided

                        i. Telencephalon

                        ii. Diencephalon

            b. Hindbrain divides

                        i. Metencephalon

                        ii. Myelencephalon

B. Brain structures associated with the developmental vesicles

            a. Telencephalon

                        i. Cerebrum

            b. Diencephalon

                        i. Hypothalamus

                        ii. Thalamus

                        iii. Epithalamus

            c. Mesencephalon

                        i. Midbrain

            d. Metencephalon

                        i. Pons

                        ii. Cerebellum

            e. Myelencephalon

                        i. Medulla oblongata