CHAPTER 13: NERVOUS SYSTEM (SPINAL AND SPINAL NERVES)

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Dermatome

- an area of the skin that provides sensory input to the CNS via one pair of spinal nerves or cranial nerve V (the trigeminal nerve, which goes to the face and scalp)

Filum terminale

- anchors the spinal cord to the coccyx

Three columns of white matter

- anterior (ventral) white columns - posterior (dorsal) white columns - lateral white columns

Two grooves divide the cord into right and left sides

- anterior median fissure - posterior median sulcus

Spinal nerves

- are part of the PNS - connect the CNS to sensory receptors, muscles, and glands in all parts of the body - 31 pairs

ages 4-5

- at ________ the spinal cord stops growing - the vertebral column continues to elongate

Roots

- bundles of axons connect each spinal nerve to a segment of the spinal cord - two roots * posterior (dorsal) * anterior (ventral)

Motor neuron

- carries the impulse triggered by the integrating center out of the CNS to the responding part

First-order neuron

- cell bodies are in the posterior (dorsal) root ganglia of the spinal nerves

The principal plexuses

- cervical plexus - brachial plexus - lumbar plexus - sacral plexus - coccygeal plexus

Nuclei

- clusters of cell bodies in the gray matter of the brain and spinal cord

Rami communicantes

- components of the autonomic nervous system

Impulses

- conducted along the posterior column-medial lemniscus pathway give rise to the following sensations - fine touch - stereognosis - proprioception - vibratory sensations

First-order neuron

- connects a receptor of the neck, trunk, or limbs with the spinal cord * the cell body is in the posterior root ganglion

Motor (descending) tracts

- consist of axons that carry impulses down the spinal cord

Sensory (ascending) tracts

- consist of axons that conduct impulses towards the brain

Posterior (dorsal) gray horns

- contain cell bodies and axons of interneurons as well as axons of incoming sensory neurons

Anterior (ventral) gray horns

- contain cells bodies of somatic motor neurons going to skeletal muscle - the neurons provide impulses for contraction of skeletal muscles

Anterior (ventral) roots

- contains axons of motor neurons - the neurons conduct impulses from the CNS to effector organs/cells

Each column

- contains bundles of axons * tracts (fasiculi) - sensory (ascending) tracts - motor (descending) tracts

Posterior (dorsal) roots

- contains only sensory axons - conduct impulses from sensory receptors to the CNS - has a swelling _________ _____ ganglion contains the cell bodies of sensory neurons

Anterior (ventral) root

- contains the axons of multipolar motor neurons - the cell bodies of these motor neurons are located in * the gray matter of the spinal cord

Posterior (dorsal) root

- contains unipolar sensory axons - contains a posterior root ganglion * where the cell bodies of sensory neurons are located

Spinal cord and spinal nerves

- contribute to homeostasis by providing quick, reflexive responses to many stimuli

Anterior spinothalamic tract

- conveys impulses for tickle, itch, crude touch, pressure, vibrations

Lateral corticospinal tract

- conveys impulses from the motor cortex to skeletal muscles on the opposite side - provides precise voluntary movements of limbs, hands, and feet - axons of upper motor neurons descend from the precentral and postcentral gyri of the cortex into the medulla

Lateral spinothalmaic tract

- conveys sensory impulses for pain and temperature

The second-order neuron

- crosses to the opposite side of the spinal cord * i.e., it decussates - It then passes upward to the brain stem in either the lateral or anterior spinothalamic tract

Anterior median fissure

- deep, wide - on anterior side

The anterior and posterior horns

- divide the white matter on each side into three columns

(Intercostal (Thoracic) Nerves) The anterior rami of T2-T12 `

- do not enter into the formation of plexuses - They are known as intercostal nerves - Directly innervate intercostal muscles and skin

Connective tissue coverings of spinal nerves

- endoneurium - perineurium - epineurium

Conus medullaris, L-1 and L-2 (in adults)

- ends at the level of the intervertebral disc between___and ___ (in adults)

The first-order neurons

- extend from sensory receptors in the trunk and limbs into the spinal cord - ascend to the medulla oblongata (on the same side of the body)

Gray commissure

- forms the crossbar of the H

(Other nerves arising in this plexus) The pudendal nerve

- goes to the muscles of the perineum, - skin of the penis - scrotum, - clitoris, - labia majora - minora, - vagina

Interneurons (association neurons)

- help with the integration of sensory information in the CNS - allows the initiation of motor responses at several levels

Lateral corticospinal tract

- in the medulla, 90% of these axons decussate and then enter the contralateral side of the spinal cord to form the _______ __________ _____

Gray horns

- includes * anterior (ventral) gray horns * lateral gray horns * posterior (dorsal) gray horns

Endoneurium

- innermost layer - wraps individual axons - whether myelinated or not

Polysynaptic reflex arc

- involves more than two types of neurons and more than one CNS synapse

Filum terminale

- is contained within the tubular sheath of dura mater, and is surrounded by spinal nerve roots forming the cauda equina

The fourth ventricle

- is in the medulla oblongata - at the superior end ( of the Central canal) , is continuous with the

The spinal cord

- is the pathway for sensory input to the brain and motor output from the brain the white matter contains a dozen major sensory (ascending) and motor (descending) tracts

Central canal

- located in the center of the gray commissure - extends the entire length of the spinal cord - at the superior end, is continuous with the fourth ventricle * the fourth ventricle is in the medulla oblongata - contains cerebral spinal fluid (CSF)

The anterior spinothalamic tract

- location = anterior white column - begins in the spinal cord - ends in the thalamus

White matter tracts

- make up the different regions (columns) of white matter surrounding the gray matter - are bundles of ascending and descending myelinated axons

The spinal cord has two functions

- nerve impulse propagation - integration of information

Two Main Function of the spinal cord

- nerves impulses propagation - information integration

The third-order

- neurons project into the primary somatosensory area of the cerebral cortex on the same side as the thalamus

Filum terminale

- non-nervous fibrous tissue of the spinal cord - extends inferiorly from the conus medullaris to the coccyx - an extension of the pia mater

Autonomic (visceral) reflexes

- not consciously perceived - involve responses of smooth muscle, cardiac muscle, and glands

Integrating center

- one or more regions of gray matter in the CNS - simplest: a monosynaptic reflex arc * a single synapse between a sensory neuron and a motor neuron

Spinal nerves

- originate from the spinal cord from the posterior (dorsal) and anterior (ventral) roots

12 (T1-T12)

- pairs of thoracic nerves

Branches = rami (singular, ramus)include

- posterior (dorsal) ramus - anterior (ventral) ramus - meningeal branch - rami communicantes

Lateral gray horns

- present only in the thoracic, upper lumbar, and sacral segments of the spinal cord - contain cell bodies of autonomic motor neurons * regulate the activity of smooth and cardiac muscles and glands

The gray matter

- processes reflexes - of the spinal cord also is a site for integration (summing) of excitatory postsynaptic potentials (EPSPs) and inhibitory postsynaptic potentials (IPSPs)

The spinal cord

- promotes homeostasis by conducting impulses along tracts

Sensory neuron

- propagates the impulse to the gray matter of the spinal cord or brain stem

Motor nuclei

- provide output to effector tissue via motor neurons

Sensory nuclei

- receive input from receptors via sensory neurons

Gray matter

- receives and integrates incoming and outgoing information

Gray matter

- receives and integrates incoming and outgoing information consists of cell bodies, dendrites, unmyelinated axons, and axon terminals

Meningeal branch

- reenters the vertebral canal via the intervertebral foramen - supplies * the vertebrae, * vertebral ligaments, * blood vessels of the spinal cord, and meninges

Gray horns

- regions of gray matter on each side of the spinal cord

Sensory receptor

- responds to stimuli by producing an action potential

Five functional components of a reflex arc

- sensory receptor - sensory neuron - integrating center - motor neuron - effector

Posterior (dorsal) ramus

- serves deep muscle and skin of the dorsal surface of the trunk

Anterior (ventral) ramus

- serves the muscles and structures of the limbs and skin of the lateral and ventral surfaces of the trunk

Posterior median sulcus

- shallower, narrow furrow - on posterior side

Gray matter

- shaped like an H or a butterfly - consists of * cell bodies of neurons * neuroglia * unmyelinated axons * dendrites of interneurons * motor neurons

Types of reflexes

- spinal reflex * integration takes place in the spinal cord gray matter - cranial reflexes * integration occurs in the brainstem - somatic reflexes * involve contraction of skeletal muscles

Two main sensory (ascending) routes

- spinothalamic tracts - posterior columns (each consisting of two tracts)

Median nerve

- supplies most of the muscles of the anterior forearm and some of the muscles of the hand

Ulnar nerve

- supplies the anteromedial muscles of the forearm and most of the muscles of the hand

Axillary nerve

- supplies the deltoid and teres minor muscles

Musculocutaneous nerve

- supplies the flexors of the arm

Radial nerve

- supplies the muscles of the posterior aspect of the arm and forearm

Cranial meninges

- surround and encircle the brain

Spinal meninges

- surround the spinal cord

White matter

- surrounds gray matter - consists primarily of bundles of myelinated axons of neurons

Two-point discrimination

- the ability to discern that two nearby objects touching the skin are truly two distinct points, not one

Stereognosis

- the ability to recognize size, shape, and texture of an object by touching it

Proprioception

- the awareness of the precise position of body parts * kinesthesia- the awareness of directions of movement * weight discrimination

Lumbar enlargement,T-9 to T-12

- the inferior enlargement - extends from ___to ___ - where nerves to and from the lower limbs arise

The sciatic nerve

- the largest nerve in the body - arises in the sacral plexus

Proprioception

- the perception of the position of body parts, especially the limbs, independent of vision

Two main routes on each side of spinal cord

- the posterior column medial lemniscus pathway - the spinothalamic tracts

Discriminitive touch

- the recognition of the location, shape, size, and texture of mechanical objects that contact skin

Epidural space

- the space between the dura mater and the wall of the vertebral canal - contains a cushion of fat and connective tissue

In newborns

- the spinal cord extends from the Medulla oblongata to the third or fourth lumbar vertebra

In adults

- the spinal cord extends from the Medulla oblongata to the top of the second lumbar vertebra

Cauda equina

- the spinal cord is shorter than the vertebral column - the roots of these spinal nerves exit the vertebral column lower than they exit from the spinal cord

Cervical enlargement, C-4 to T-1

- the superior enlargement - extends from_to ___ - where nerves to and from the upper limbs arise

Conus medullaris

- the tapered portion of the spinal cord inferior to the lumbar enlargement

Lateral corticospinal tract

- the upper motor neurons end in the anterior gray horn on the same side - they provide input to the lower motor neurons, which innervate skeletal muscles

Vertebral canal (Vertebral column)

- the vertebral foramina of the vertebrae form the _________ _____ - the spinal cord is located within the_________ _____

Axon terminals synapse

- with second-order neurons whose cell bodies are located in the gracile nucleus or cuneate nucleus of the medulla

Perineurium

- wraps fasicles - bundles of axons

Posterior (dorsal) columns

-In the spinal cord, axons form the_________(dorsal) _______ - two parts * gracile fasiculus * cuneate fasiculus

White matter

-The cord's ____ ______ is organized into regions called columns

Meninges (singular, meninx)

-Three connective tissue coverings that encircle the brain and spinal cord are called * spinal meninges surround the spinal cord * cranial meninges surround and encircle the brain

8 (C1-C8)

-_ pairs of cervical nerves

5 (S1-S5)

-_ pairs of sacral nerves

Gray matter

-____ _____of the spinal cord receives and integrates incoming and outgoing information

Anterior (ventral) white commissure

-anterior to the gray commissure - connects the white matter of the right and left sides of the spinal cord

The second-order

-axons end in the ventral posterior nucleus of the thalamus

Epineurium

-the superficial covering of the entire nerve - fuses with the dura mater of the spinal meninges as the spinal nerve passes through the intervertebral foramen

Motor output to skeletal muscles

-travel down two types of descending pathways * direct (pyramidal) pathways * indirect (extrapyramidal) pathways

* bony vertebrae * meninges

-two types of connective tissue coverings protect the spinal cord

Indirect (ExtraPyramidal) Pathways

* also maintain skeletal muscle tone and contraction of postural muscles * play a role in equilibrium by regulating muscle tone in response to head movements

Pia mater

- "delicate mater" Inner - the inner most meninx - a thin transparent connective tissue layer that adheres to the brain and spinal cord - consists of interlacing bundles of collagen fibers and some fine elastic fibers

Cauda equina

- "horse's tail" - roots of spinal nerves that arise from the lumbar, sacral and coccygeal region

Arachnoid mater

- "spider like" middle - the middle meninx - an avascular covering - a spider web arrangement of delicate collagen fibers and some elastic fibers - continuous with the arachnoid mater of the brain

Dura mater

- "tough mother" Outer - the most superficial meninx - a sac of dense irregular connective tissue - extends from the foramen magnum to the second sacral vertebra - is continuous with the dura mater of the brain

Posterior Column-Medial Lemniscus Pathway

- A pathway in the posterior columns

Spinal nerve

- A typical ______ _____has two connections to the cord posterior (dorsal) root anterior (ventral) root

Spinal nerves

- All ______ ______and their branches are part of the PNS - connect the CNS to sensory receptors, muscles, and glands - are 31 pairs of mixed nerves * have both motor and sensory fibers

Anterolateral (Spinothalamic) Tracts

- Are composed of thousands of sets of three neurons * first-order neurons * second-order neurons * third-order neurons

Spinal Nerves

- Are named/numbered according to the region and level of the vertebral column from which they emerge

Posterior Columns

- Carry impulses for * proprioception * discriminative touch * two-point discrimination * light pressure sensation s * vibration sensation

Indirect (ExtraPyramidal) Pathways

- Convey impulses from the brain stem and other parts of the brain * impulses govern automatic movements and help coordinate body movements with visual stimuli * also maintain skeletal muscle tone and contraction of postural muscles

Direct (Pyramidal) Pathways

- Convey impulses that originate in the cerebral cortex - Eventually cause precise voluntary movements of skeletal muscles

bundles of axons (tracts)

- Each column contains ______ __ ______ (tracts) that have a common origin or destination and that carry similar information

Cervical Plexus

- Formed by the Anterior (ventral) rami of C1-C4 and part of C5

Brachial Plexus

- Formed by the anterior (ventral) rami of C5-C8 and T1 - Lateral to the last 4 cervical and first thoracic vertebrae - Provides the entire nerve supply of the shoulders and upper limbs

Lumbar Plexus

- Formed by the anterior (ventral) rami of spinal nerves L1-L4 - On either side of the first four lumbar vertebrae

Sacral Plexus

- Formed by the anterior (ventral) rami of spinal nerves L4-L5 and S1-S4 - is anterior to the sacrum - supplies the buttocks, perineum, and lower limbs

Coccygeal Plexus

- Formed by the anterior (ventral) rami of spinal nerves S4-S5 and the coccygeal nerves - Supplies a small area of the skin in the coccygeal region

Posterior columns

- Gracile fasciculus - Cuneata fasciculus

Cuneate fasiculus

- Impulses from the neck, upper limbs, and upper chest propagate along axons in the _______ _________and arrive at the cuneate nucleus

Thalamus

- In the ________ the axon terminals of second-order neurons synapse with third-order neurons * project their axons to the primary somatosensory area of the cerebral cortex

Direct (Pyramidal) Pathways

- Include the lateral corticospinal - anterior corticospinal - corticobulbar tracts

Indirect (ExtraPyramidal) Pathways

- Include the rubrospinal - tectospinal - vestibulospinal tracts

Cervical Plexus

- Is alongside the 4 cervical vertebrae on both sides - Supplies the skin and muscles of the head, neck, and superior parts of the shoulders and chest

spinal cord (or which) spinal nerve

- Knowledge of dermatomes helps physicians determine which segment of the______ ____or which______ _____is damaged

Plexuses

- Most spinal nerves are arranged in ________

Lateral Gray Horns

- Motor neuron pathways in the autonomic nervous system

Anterior Gray Horns

- Motor neuron pathways in the somatic nervous system

Posterior Columns

- Right and left - each side contains two tracts (fasiculi) * gracile fasiculus * cuneate fasiculus

Spinal nerves branch

- Soon after leaving the intervertebral foramen, ______ ______ ______ - branches = rami (singular, ramus)

Types of Reflexes

- Stretch Reflex - Tendon Reflex - Flexor (Withdrawal) Reflex - Crossed Extensor Reflex

Lumbar Plexus

- Supplies the anterolateral abdominal wall, external genitals, and part of the lower limbs

Phrenic nerves

- The _______ ______arise from the cervical plexuses and supply motor fibers to the diaphragm

Medial lemniscus

- The axon of the second-order neuron crosses to the opposite side of the medulla and enters the ________ __________ * a ribbon-like tract that extends form the medulla to the thalamus

Cervical pair

- The first ________ ____emerge between the atlas and the occipital bone

Crossed extensor reflex

- The flexor reflex arc is shown at left for comparison with the crossed extensor arc.

Lumbar Plexus

- The largest nerve arising in this plexus is the femoral nerve - goes to the flexor muscles of the thigh and the extensor muscles of the leg

Reflex Arc (Reflex Circuit)

- The pathway followed by nerve impulses that produce a reflex

Intervertebral foramen

- The posterior and anterior roots unite to form a spinal nerve at the ________ ________ * spinal nerves are mixed nerves

Thorax

- There is no plexus formation in the ______ - there are no limbs in this area

Stretch reflex

- This monosynaptic reflex arc has only one synapse in the CNS--between a single sensory neuron and a single motor neuron. A polysynaptic reflex arc to antagonistic muscles that includes two synapses in the CNS and one interneuron is also illustrated.

Flexor (withdrawal) reflex

- This reflex arc is polysynaptic and ipsilateral. Plus signs (+) inidcate excitatory synapses.

Tendon reflex

- This reflex arc is polysynaptic-- more than two different neurons are involved in the pathway. The sensory neuron synapses with two interneurons. An inhibitory interneuron causes relaxation of the effector, and a stimulatory interneuron causes contraction of the antagonistic muscle.

1

- _ pair of coccygeal nerves

5 (L1-L5)

- _ pairs of lumbar nerves

The anterior rami

- ___ ________ ____ of the spinal nerves (except T2-T12) do not go directly to body structures * they form plexuses

All others

- ___ ______emerge from the vertebral column - through the intervertebral foramina between vertebra

White matter tracts

- ____ _____ _____ in the spinal cord are highways for nerve impulse generation

Motor

- _____ (descending) tracts propagate impulses from the brain down the spinal cord towards effectors - are part of somatic motor pathways

Nerve impulses

- _____ _______from sensory receptors propagate up the spinal cord along two main routes on each side

Sensory

- _______ (ascending) tracts propagate impulses from sensory receptors up the spinal cord to the brain - are part of somatic sensory pathways

In the brain

- a cushion of cerebral spinal fluid (CSF) produced __ ___ _____ * surrounds and protects the spinal cord

Filum terminale

- a delicate filament, about 20 cm. in length - extends downward from the apex of the conus medullaris

Reflex

- a fast, involuntary, unplanned sequence of actions that occurs in response to a particular stimulus - some are inborn * pulling a hand away from a hot object - some are learned * slamming on the brakes

Plexus

- a network of axons - an area where fibers join and resort so that each nerve leaving the plexus contains all the fibers that innervate a particular region of the body

Plexus

- a network of nerves, veins, or lymphatic vessels

Subarachnoid space

- a space between the arachnoid and pia maters contains CSF

Subdural space

- a thin space between the dura mater and arachnoid mater contains interstitial fluid

Injuries to the brachial plexus

- affect the sensations and movements of the upper limbs. A; Erb-Duchene Palsy (waiters tip) B; Waist drop C; Median nerve palsy D; Ulnar nerve palsy E; winging of right scapula

Somatic Motor (Descending) Tracts

Conduct impulses FROM the brain (primary motor region of the precentral gyrus) to skeletal muscle

Brachial Plexus

Five important nerves arise in this plexus - axillary nerve - musculocutaneous nerve - Radial nerve - Median nerve - Ulnar nerve

Gracile fasiculus

Impulses from the trunk and lower limbs propagate along axons in the _______ _________ and arrive at the gracile nucleus

(Other nerves arising in this plexus) The superior and inferior gluteal nerves

Other nerves arising in this plexus * go to the gluteus muscles

tract

The name of a _____ is descriptive - indicates position - indicates where it begins and ends Example: the anterior spinothalamic tract

three sets

There are _____ ____ of columns : right and left anterior (ventral) white columns, right and left posterior (dorsal) white columns, and right and left lateral white columns

(The meninges) dura mater , arachnoid mater , pia mater

Three connective tissue coverings - "tough mother" Outer - "spider like" middle - "delicate mater" Inner

Effector

_ if it's a somatic reflex, the effector is skeletal muscle - if its an autonomic reflex, the effector is smooth muscle, cardiac muscle, or a gland

White matter tracts

function as "highways" for nerve impulse propagation


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