Ch. 13 lecture spinal cord and spinal nerves

dermatomes

Certain segments of the skin are supplied by spinal nerves that carry somatic sensory nerve impulses to the brain • overlaps, knowing which spinal cord segments supply each ___ makes it possible to locate damaged regions of spinal cord.

cerebral cortex

outer part of brain, plays a major role in controlling precise voluntary muscular movements

gray matter of spinal cord

receives and integrates incoming and outgoing information

gray matter of spinal cord

serves as the integrating center of spinal reflexes

muscle tone

which is small degree of contraction

sensory and motor tracts

• Communication to and from the brain involves tracts • Ascending tracts are sensory - Deliver information to the brain • Descending tracts are motor -Deliver information to the periphery

disorders

• Spinal cord compression (may result from fracture vertebrae or herniated discs, tumors, osteoporosis • Degenerative diseases (multiple sclerosis) • Shingles ( infection of PNS caused by herpes zoster, virus retreats to a posterior Rott ganglion, blisters • Poliomyelitis ( poliovirus, produces paralysis by destroying cell bodies of motor neurons

spinal nerves

• connect the CNS to sensory receptors, muscles, and glands and are part of the peripheral nervous system • 31 pairs of spinal nerves • Anterior and posterior roots attach a spinal nerve to a segment of the spinal cord • are the paths of communication between the spinal cords and specific regions of the body

intersegmental reflex

• nerve impulses from one sensory neuron ascend and descend in the spinal cord and activate interneurons in several segments of spinal cord

ipsilateral reflex

• sensory nerve impulse enter the spinal cord on the same side from which motor nerve impulses leave

reciprocal innervation

• when stretched muscle contracts during a stretch reflex, an antagonistic muscles that oppose the contraction relax • THIS TYPE OF ARRANGEMENT IN WHICH COMPONENTS OF NEURAL CIRCUIT STIMUTANEOSLY CAUSE CONTRACTION OF ONE MUSCLE AND RELAXATION OF ITS ANTAGONISTS IS CALLED.

autonomic reflexes

• which are not consciously perceived. • involve responses of smooth muscle, cardiac muscle, digestion, urination, and defecation which are controlled by ANS through these ____

reflexes and reflex arcs

•A reflex is a fast, involuntary, unplanned response to a particular stimulus •Reflexes help maintain homeostasis • The gray matter of the spinal cord serves as the integrating center for spinal reflexes

Spinal Cord Physiology

•In order to maintain homeostasis, the spinal cord must propagate nerve impulses and integrate information •How does information travel in the spinal cord? •White matter tracts conduct nerve impulses to and from the brain •Gray matter receives and integrates incoming and outgoing information to perform spinal reflexes

spinal cord functions

•The white matter of the spinal cord contains sensory and motor tracts, the "highways" for conduction of sensory nerve impulses toward the brain and motor nerve impulses from the brain toward effector tissues. •The spinal cord gray matter is a site for integration (summing) of excitatory postsynaptic potentials (EPSPs) and inhibitory postsynaptic potentials (IPSPs). •Spinal nerves and the nerves that branch from them connect the CNS to the sensory receptors, muscles, and glands in all parts of the body.

monosynaptic reflex

•a reflex pathway having only one synapse in the CNS • 2 neurons and one synapse • ALL ____ are ipsilateral

crossed extensor reflex

maintains balance during a withdrawal reflex • polysynaptic • contralateral reflex arc: opposite side: sensory impulses enter one side of spinal cord and motor impulses exit on opposite side. • reciprocal innervation occurs in both flexor and and crossed extensor reflex (one set of muscles contracts the other relaxes

somatic reflexes

involve contraction of skeletal muscles

polysynaptic reflex

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

reflex

is a fast involuntary, unplanned sequence of actions that occurs in response to a particular stimulus • some are inborn such as pulling your hand away from a hot surface • others are learned or aquired. for instance you learn ___ when driving (slamming on breaks in an emergency) • when integration takes place in spinal cord gray matter it is spinal ___ • if integration occurs in brainstem rather than spinal cord, ___ is called cranial

sensory system

keeps CNS informed of changes in the external and internal environments. • sensory information is integrated (processed) by interneurons in the spinal cord and brain

ventral root

contain axons of motor neurons, which conduct nerve impulses from CNS to effectors (muscles & glands)

dorsal roots

contain only sensory receptors in the skin, muscles and internal organs into CNS

protection of spinal cord

1) first layer of protection is the hard bony skull and vertebral column 2) meninges, three membranes that lie between the bony encasement and the nervous tissue in Both the brain and spinal cord 3) CSF: a space between two meningeal membranes contains CSF a buoyant liquid that suspends the CNS nervous tissue in a weightless environment while surrounding it with a shock absorbing, hydraulic cushion

internal organization of spinal cord

1) sensory receptors detect a stimulus 2) sensory neurons convey this sensory input in form of nerve impulses 3) axons of sensory neurons extend into white matter of spinal cord 4) axons extend into into gray matter and synapse with interneurons 5) turn synapse with somatic motor neurons that involved in spinal reflex pathways 6) motor output from spinal cord to skeletal muscles involves somatic neurons 7) when activated, somatic neurons convey motor motor output in the from of nerve impulses along their axons

functions of spinal cord

1. Processes reflexes 2. Integrates EPSPs and IPSPs 3. Conducts sensory impulses to the brain and motor impulses to effectors

components of reflex arc

1. sensory receptor (dendrite responds to a specific stimulus: a change in internal or external environment) 2. sensory neuron: nerve impulse propagates from sensory receptor to axon terminal 3. integration center( gray matter within in the CNS) 4. motor neuron (impulses triggered by integration center propagate out of CNS along a motor neuron to part of the body that will respond) 5. effector (the part of the body that responds to morrow nerve impulse, such as muscle or gland

sensory and motor processing

The internal anatomy of the spinal cord allows sensory and motor information to be processed in an organized way

white matter tracts of spinal cord

are highways for nerve impulse propagation. sensory input travels from the brain and motor output travels from the brain along these tracts toward skeletal muscles and other effectors

flexor (withdrawal) reflex

causes withdrawal of a limb to avoid injury or pain • involves polysynaptic reflex arc 1) painful heat stimulus activates thermal pain receptor in finger 2) action potentials are generated in afferent pathway which propagates impulses to spinal cord 3) spinal cord serves as integrating center: a) excitatory neurons which stimulate motor neurons to biceps b) inhibitory interneurons, which inhibit motor neurons to triceps c) interneurons that are part of ascending pathway to brain 4) one efferent pathway stimulates biceps to contract other efferent pathway leads to relaxation of triceps by preventing counterproductive excitation and contraction of this antagonistic muscle 5) the biceps and triceps are effectors, resultant flexion of elbow joint pulls hands away from painful stimulus(withdrawal reflex) 6) events that occur in brain on arrival of signal via ascending pathway, such as awareness of pain, memory storage, and so on • reflex arcs can be influenced by descending pathways from brain • also called an intersegmental reflex

stretch reflex

•causes contraction of a muscle (the effector) that has been stretched • occurs monosynaptic (only one synapse in CNS) reflex arc • can be elicited by tapping tendons at elbow, wrist, knee, and ankle joints. • ___ is stretching of muscle, this reflex helps avert injury by preventing over stretching of muscles 1) slight stretching of muscle stimulates sensory receptors in the muscle called muscle spindles 2) in response to being stretched, a muscle spindle generates one or more nerve impulses that propagate along a somatic sensory neuron through posterior root of spinal nerve in spinal cord 3) in the spinal cord (integrating center), the sensory neuron makes an excitatory response and thereby activates a motor neuron in the anterior gray horn 4) if excitation is strong enough, one or more nerve impulses arises in the motor neuron and propagates, along its axon. the axon terminals of motor neuron form NMJ with skeletal muscle fibers of stretched muscle 5) ACH relased by nerve impulses at NMJ triggers one or more muscle Action potentials in the stretched muscle (effector) and the muscle contracts. SO MUSCLE STRECH IS FOLLOWED BY MUSCLE CONTRACTION, WHICH RELIEVES STRETCHING

tendon reflex

•causes relaxation of the muscle attached to the stimulated tendon • operates as a feedback mechanism to control muscle tension by causing muscle relaxation (in contrast stretch reflex operates to control muscle length by causing muscle contraction). before muscle force becomes so great that tendons might be torn • is polysynaptic (more than one CNS synapse and 2 different neurons involved in the pathway. • is ipsilateral just like stretch) • although this ___ reflex is less sensitive than stretch reflex, it can override the stretch reflex when the tension is great, making you drop a heavy weight for ex.

tramatic injuries

•monoplegia (paralysis of one limb) paraplegia (paralysis of both lower limbs hemiplegia ( is paralysis one side of the body) quadriplegia ( paralysis of all four limbs) • Damage that results from traumatic injuries depends on: - Degree of spinal cord section or - Degree of compression of the segments involved