CHAPTER 13: NERVOUS SYSTEM (SPINAL AND SPINAL NERVES)
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
