spinal cord and spinal nerves

what does this describe:

extends inferiorly from brains medulla through verterbral canal

four parts: cervical, thoracic, lumbar, and sacral

ends at L1 vvertebrae with conus medullaris

spinal nerve roots extend inferiorly = cauda equina

2 widened regions with greater number of neurons

spinal cord

cervical enlargement

neurons innervating upper limbs

lumbar enlargment

neurons innervating lower limbs

sensory input from body to brain

afferent conduction

motor commands from brain to body

efferent conduction

neural integration

minimal: most thinking, porcessing and deciosion making occurs at level of the brain

reflexes

responses that do not involve the brain

goes cervical, thoracic, lumbar, sacral

know cauda equina and conus medullaris

be able to label

nerve

cablelike bundle of axons

what are the 3 kinds of connective tissue wrappings around nerves and what are they like:

epineurium (around nerve)

perineurium (around fascicle)

endoneurium (around axon)

what does this describe:

rootlets merge to form roots

posterior root contains sensory neurons

posterior root ganglion contains cell bodies of these neurons

each spinal nerve forms where the roots join

sensory and motor neurons in each spinal nerve so they are classified as mixed nerves

spinal nerve gross anatomy

what things are the spinal cord protected by

bone, meninges and cerebrospinal fluid

____ houses the spinal cord

cord passes through the vertebral canal

each spinal nerve exits through an intervertebral foramen

vertebral column

what spinal cord meninge does this describe:

delicate layer adhering to spinal cord

made of elastic and collagen fibers

denticulate ligaments: lateral extensions of pia; help suspend spinal cord

filum terminale: pia anchoring inferior end of spinal cord to coccyx

pia mater

what spinal cord meninge does this describe:

web-like ayer, external to pia

arachnoid trabeculae: fibrous extensions of the membrane

subarachnoid space: area deep to arachnoid through which CSF flows

arachnoid mater

what spinal cord meninge does this describe:

tough, outmost layer

one layer of dense irregular connective tissue that stabilizes spinal cord

subdural space: is between dura and arachnoid

epidural space: is between dura and vertebra; houses adipose, areolar connective tissue, blood vessels

dura mater

lumbar puncture

procedure for obtaining CSF for medical diagnosis

needle passes through skin, back muscles, ligamentum flavum, epidural space, dura mater, arachnoid mater into subarachnoid space

adult spinal cord ends at L1; puncture below;

grey matter

made of neuron’s cell bodies, dendrites, and unmyelinated axons; also glial cells

masses of grey. matter project from center of spinal cord

posterior horns

house axons of sensory neurons and cell bodies of interneurons

anterior horns

house cell bodies of somatic motor neurons

lateral horns

house cell bodies of autonomic motor neurons; only in T1-L2

gray commissure

horizontal band of grey matter surrounding central canal

contains unmyelinated axons connecting left and right gray matter

nuclei

groups of cell bodies

somatic sensory nuclei

receive signals from skin, muscle, joints

visceral sensory nuclei

receive signals from bloods vessels, viscera

somatic motor nuclei

anterior horns

innervate skeletal muscle

autonomic motor nuclei

lateral horns

innervate smooth muscle, heart, glands

know this pic

white matter

myelinated axons to and from the brain

posterior funiculus

contains sensory tracts

axon bundles called fasciculi

signals about proprioception, touch, pressure, and vibration with a 3 neuron chain

lateral funiculus

contains sensory (ascending) and. motor (descending) tracts

anterior funiculus

contain sensory (ascending) and motor (descending) tracts

axons are in ______ _____ tracts

cell bodies and in _______, _________, and ___________

spinal cord

ganglia, spinal cord gray horns, and brain gray matter

sensory input transmitted through spinal cord originates from general sense receptors

primary (1st order) neuron: has peripheral ending, cell pody. in posteiror root ganglion, and axon leading to secondary neruon

secondary (2nd order) neuron: is an interneuron, receives primary input and extends to tertiary neuron or to cerebellum

tertiary (3rd order): is an interneuron, receives secondary neuron input and extends to somatosensory cortex of parietal lobe or cerebrum

sensory pathways

somatic sensory (somatosensory) receptors

tactile: detect characteristics of an object

proprioceptors: detect stretch in joints, muscles, tendons

carry signals from skin, muscles, and joints

visceral sensory receptors

detect changes like stretch in an organ

carry signals from viscera

what does this describe:

signals about proprioception, touch, and vibration with a 3-neuron chain

primary neuron relays signal from skin to brainstem

secondary neuron relays signal from medulla to thalamus

tertiary neuron relays signal to primary somatosensory cortex (postcentral gyrus)

posterior funiculus - medial lemniscal pathway

what does this describe:

signals related to crude tough, pressure, pain and temperature with a 3 neuron chain

primary neuron relays signal from skin to spinal cord

secondary neuron relays signal from spinal cord to thalamus

tertiary neuron relays signal from thalamus to cerebral cortex

anterolateral pathway

what does this describe:

signals about proprioception with a 2-neuron chain

primary neuron relays signal from skin to spinal cord

secondary neuron relays signal from spinal cord to cerebellum

spinocerebellar pathway

what does this describe:

control effectors such as skeletal muscles

start in brain and include at least 2 neurons

motor pathways

in motor cortex, cerebral nucleus, or brainstem nucleus; contacts lower motor neuron

upper motor neuron

in cranial nerve nucleus or spinal cord anterior horn; excites muscle

lower motor neuron

pathway between brain and skeletal muscles

direct (pyramidal) pathway

what does this describe:

upper motor neurons originate in brainstem nuclei and take complicated route to spinal cord

indirect pathway

what kind of indirect motor pathway does this describe:

regulates precise movement and tone in flexor limb muscles

consists of rubrocpinal tracts originating in midbrain

lateral pathway

what kind of indirect motor pathway does this describe:

regulates muscle tone and movements of head, neck, proximal limb, trunk

medial pathway

what does this describe:

from reticular formation

help control reflexes related to posture and balance

reticulospinal tracts

what does this describe:

from superior and inferior colliculi

regulate reflexive orienting responses to visual and auditory stimuli

tectospinal tracts

what does this describe:

from vestibular nuclei of brainstem

help maintain balance during sitting, standing, walking

vestibulospinal tracts

how can you treat spinal cord injuries

prompt use of steroid after injury may preserve muscle function

early antibiotics have reduced number of deaths due to pulmonary and urinary infections

neural stem cells may be used in the future to regenerate CNS axons

dermatomes

segment of skin supplied by single spinal nerve

some overlap in innervated regions

can help localize damage to one or more spinal nerves

involved in referred visceral pain

shingles

reactivation of chickenpox infection

virus remaining latent in posterior root ganglia

reactivated, travels through sensory axons to dermatome

rash and blisters along the dermatome

burning and tingling pain

antiviral medication to reduce sensitivity

vaccine to prevent or reduce disease sensitivity

what does this describe:

network of interweaving anterior rami of spinal nerves

four main plexuses occur bilaterally: cervical, brachial, lumbar, and sacral

individual rami branch repeatedly (damage to one nerve or spinal segment does not deprive a muscle or skin region of all innervation)

nerve plexuses

what does this describe:

anterior rami of C1-C4

branches innervate: anterior neck muscles, skin of neck, portions of head and shoulders

from rami of C3-C5 it gives rise to phrenic nerve

cervical plexuses

what does this describe:

from anterior rami of C5-T1

trunks divide into anterior and posterior divisions

axons innervate anterior and posterior parts of upper limbs

brachial plexuses

brachial plexus injuries

minor injuries treated with rest

severe injuries may require nerve grafts or transfers

axillary; compressed axilla or damaged, difficulty abducting arm

radial: humeral shaft fractures or injuries to elbow, paralysis of extensor muscles in forearm, numbness along posterior arm

posterior cord:may be injured by improper use of crutches

what does this describe:

anterior rami of L4-S4

sciatic nerve: largest and longest nerve in the body, formed from portions of anterior and posterior sacral plexus, composed of tibial division and common fibular division

sacral plexuses

tibial nerve in sacral plexus

from anterior division of sciatic

innervates hamstrings and hamstring part of adductor magnus muscle

splits into lateral and medial parts

receives sensory signals from skin on sole of foot

common fibular nerve

from posterior division of sciatic

innervates short head of biceps femoris muscle

splits into deep fibular nerve and superficial fibular nerve

sacral plexus injuries

superior or inferior gluteal nerves

can be injured by poorly placed gluteal injection

sciatica: injury to sciatic nerve; extreme pain down posterior thigh and leg, may be caused by herniated intervertebral disc

what does this describe:

rapid, preprogrammed, involuntary responses of muscles or glands to a stimulus

a stimulus is required to initiate

response is rapid: involves chain of few neurons

response is preprogrammed: always the same

the response is involuntary: no intent or awareness of the reflex before it happens

survival mechanism

reflexes

reflex arc

neural pathway responsible for generating the response

what is the pathway of reflex arc

1. somatic receptors: in skin, muscles or tendons

2. afferent nerve fibers: carry information from receptors to posterior horn of spinal cord or the brainstem

3. integrating center: a point of synaptic contact between neurons in gray matter; determines whether efferent neurons issue signal to muscles

4. efferent nerve fibers: carry motor impulses to skeletal muscle

5. effectors: the somatic effectors carry out the response

what are ways reflexes can be classified

spinal or cranial

somatic or visceral: is it skeletal muscle or cardiac, smooth, gland

monosynaptic or polysynaptic: direct or interneurons

ipsilateral or contralateral

innate or acquired

4 common spinal reflexes

stretch, golgi tendon, withdrawal, crossed-extensor

stretch and golgi tendon reflexes rely or ______

proprioceptors

a _____ is a proprioceptor that detects stretch in a muscle

muscle spindle

fibers not within spindle are _________ innervated by large alpha motor neurons

extrafusal muscle fibers

what does this describe:

reflexive contraction of a muscle after it is stretched

stretch is detected by muscle spindle proprioceptor

can be spinal, somatic, monosynaptic, ipsilateral, innate

when stretched, spindles sensory axon fires impulses to spinal cord, sensory axon excites alpha motor neurons causing contraction, sensory axon excites interneurons of antagonist muscle

stretch reflex

what does this describe:

prevents muscle from contracting excessively

golgi tendon organs detect excessive tension

some excited interneurons inhibit motor neurons of same muscle

some excited interneurons excite motor neurons of antagonist muscle (reciprocal activation)

golgi tendon reflex

what does this describe:

pulls body part away from painful stimulus

stimulus excites nociceptor sensory neuron that transmits signal to spinal cord and excites interneurons

interneurons excite motor neurons of flexors so flexor muscles contract and limb is withdrawn

withdrawal reflex

what does this describe:

occurs in conjunction iwth withdrawal reflex

some interneurons excited by nociceptor senesory neuron cross midline and excite extensor motor neurons on other side

allows opposite side limb to support body weight while hurt limb withdrawls

reflexes in clinical setting

useful for diagnoses

can test function of specific muscles

hypoactive reflex: diminished or absent; damage to spinal cord or muscle disease or damage to nueromuscular junction

hyperactive reflex: abnormally strong repsonse; may indicate damage to brain or spinal cord

clonus: rhythmic oscillating movements with reflex testing