Anatomy

brachial plexus

Formed by the roots (anterior rami) of spinal nerves C5-C8 and T1 - extends inferiorly and laterally on either side of the last four cervical and first thoracic vertebrae - passes above the first rib posterior to the clavicle and then enters the axilla. - supplies the shoulder and upper limbs.

cervical plexus

Formed by the roots (anterior rami) of the first four cervical nerves (C1-C4), with contributions from C5. There is one on each side of the neck alongside the first four cervical vertebrae. The cervical plexus supplies the skin and muscles of the head, neck, and superior part of the shoulders and chest and diaphragm.

fascicles

Groups of axons with their endoneurium are arranged in these bundles

cranial reflex

If integration occurs in the brain stem rather than the spinal cord, the reflex is called a... An example is the tracking movements of your eyes as you read this sentence.

conus medullaris

Inferior to the lumbar enlargement, the spinal cord terminates as a tapering, conical structure - ends at the level of the intervertebral disc between the first and second lumbar vertebrae in adults

monosynaptic reflex arc

A reflex pathway having only one synapse in the CNS - More often, the integrating center consists of one or more interneurons, which may relay impulses to other interneurons as well as to a motor neuron.

Where does a spinal nerve divide into several branches?

A short distance after passing through its intervertebral foramen

Reflex arc Step 3: Integrating centre

One or more regions of gray matter within the CNS act as an integrating center. - In the simplest type of reflex, the integrating center is a single synapse between a sensory neuron and a motor neuron.

Integrating centre

One or more regions of gray matter within the CNS play this role.

contralateral reflex arc

Sensory impulses enter one side of the spinal cord and motor impulses exit on the opposite side. - Thus, a crossed extensor reflex synchronizes the extension of the contralateral limb with the withdrawal (flexion) of the stimulated limb.

Fissure and sulcus of spinal cord

Two grooves penetrate the white matter of the spinal cord and divide it into right and left sides

roots

Two bundles of axons that connect each spinal nerve to a segment of the cord.

posterior (dorsal) root ganglion

a swelling in each posterior dorsal root which contains the cell bodies of sensory neurons.

Naming of the 31 pairs of spinal nerves

according to the region and level of the vertebral column from which they emerge

Motor output to skeletal muscles travels down the spinal cord in two types of descending pathways

direct and indirect

the three spinal meninges

dura mater, arachnoid mater and pia mater

spinal cord reflex

quick, automatic response to certain kinds of stimuli that involves neurons only in the spinal nerves and spinal cord

Reflex arc Step 1: Sensory receptor

- The distal end of a sensory neuron (dendrite) or an associated sensory structure serves as a sensory receptor. - It responds to a specific stimulus by producing a graded potential called a generator (or receptor) potential - If a generator potential reaches the threshold level of depolarization, it will trigger one or more nerve impulses in the sensory neuron.

a spinal nerve is classified as? Why?

- a mixed nerve. - Because the posterior root contains sensory axons and the anterior root contains motor axons

stretch reflex

- causes contraction of a skeletal muscle (the effector) in response to stretching of the muscle. - This type of reflex occurs via a monosynaptic reflex arc. - The reflex can occur by activation of a single sensory neuron that forms one synapse in the CNS with a single motor neuron. - Stretch reflexes can be elicited by tapping on tendons attached to muscles at the elbow, wrist, knee, and ankle joints.

principal plexuses

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

tracts

- distinct bundles of axons in the CNS having a common origin or destination and carrying similar information, located in the columns of white matter - may extend long distances up or down the spinal cord

lumbar plexus

- formed by the roots (anterior rami) of spinal nerves L1-L4 - On either side of the first four lumbar vertebrae, the lumbar plexus passes obliquely outward, posterior to the psoas major muscle and anterior to the quadratus lumborum muscle. It then gives rise to its peripheral nerves. - supplies the anterolateral abdominal wall, external genitals, and part of the lower limbs.

sacral plexus

- formed by the roots (anterior rami) of spinal nerves L4-L5 and S1-S4 - This plexus is situated largely anterior to the sacrum. - supplies the buttocks, perineum, and lower limbs. The largest nerve in the body—the sciatic nerve—arises from this plexus.

autonomic (visceral) reflexes

- generally are not consciously perceived. - involve responses of smooth muscle, cardiac muscle, and glands. - body functions such as heart rate, digestion, urination, and defecation are controlled by the autonomic nervous system through autonomic reflexes.

direct pathways

- include the lateral corticospinal, anterior corticospinal, and corticobulbar tracts. They convey nerve impulses that originate in the cerebral cortex and are destined to cause precise, - voluntary movements of skeletal muscles.

Indirect pathways

- include the rubrospinal, tectospinal, and vestibulospinal tracts - convey nerve impulses from the brain stem and other parts of the brain that govern automatic movements and help coordinate body movements with visual stimuli. - also maintain skeletal muscle tone, maintain contraction of postural muscles, and play a major role in equilibrium by regulating muscle tone in response to movements of the head.

arachnoid mater

- the middle meninx - an avascular covering - called the arachnoid mater because of its spider's web arrangement of delicate collagen fibers and some elastic fibers. - It is deep to the dura mater and is continuous with the arachnoid mater of the brain.

crossed extensor reflex

-causes contraction of muscles that extend joints in the limb opposite a painful stimulus. -helps you maintain balance just before you undergo a flexor/withdrawal reflex - contralateral reflex arc - reciprocal innervation

All monosynaptic reflexes

... they are all ipsilateral reflexes

Spinal nerves and the nerves that branch from them are part of the ...

... they're part of the peripheral nervous system.

Operation of a tendon reflex

1. As the tension applied to a tendon increases, the tendon organ (sensory receptor) is stimulated (depolarized to threshold). 2. Nerve impulses arise and propagate into the spinal cord along a sensory neuron. 3. Within the spinal cord (integrating center), the sensory neuron activates an inhibitory interneuron that synapses with a motor neuron. 4. The inhibitory neurotransmitter inhibits (hyperpolarizes) the motor neuron, which then generates fewer nerve impulses. 5. The muscle relaxes and relieves excess tension.

Five functional components of a reflex arc

1. sensory receptor 2. sensory neuron 3. integrating centre 4. motor neuron 5. effector

four important somatic spinal reflexes

1. the stretch reflex 2. the tendon reflex 3. the flexor (withdrawal) reflex 4. the crossed extensor reflex.

reflex

A fast, automatic, unplanned sequence of actions that occurs in response to a particular stimulus. - Some reflexes are inborn, such as pulling your hand away from a hot surface before you even feel that it is hot. - Other reflexes are learned or acquired. For instance, you learn many reflexes while acquiring driving expertise

reciprocal innervation

An arrangement, in which the components of a neural circuit simultaneously cause contraction of one muscle and relaxation of its antagonists. - prevents conflict between opposing muscles and is vital in coordinating body movements.

filum terminale

Arising from the conus medullaris - an extension of the pia mater that extends inferiorly and anchors the spinal cord to the coccyx.

cauda equina

Because the spinal cord is shorter than the vertebral column, nerves that arise from the lumbar, sacral, and coccygeal regions of the spinal cord do not leave the vertebral column at the same level they exit the cord. - The roots of these spinal nerves angle inferiorly in the vertebral cavity from the end of the spinal cord like wisps of hair.

lateral gray horns

Between the anterior and posterior gray horns - present only in the thoracic, upper lumbar, and sacral segments of the spinal cord. - contain autonomic motor nuclei that regulate the activity of smooth muscle, cardiac muscle, and glands.

subarachnoid space

Between the arachnoid mater and the pia mater - contains cerebrospinal fluid

subdural space

Between the dura mater and the arachnoid mater - contains interstitial fluid

rami

Branches that spinal nerves divide into

Connective Tissue Coverings of Spinal Nerves

Each spinal nerve and cranial nerve consists of many individual axons and contains layers of protective connective tissue coverings

Reflex arc Step 4: Motor Neuron

Impulses triggered by the integrating center propagate out of the CNS along a motor neuron to the part of the body that will respond.

nuclei (in spinal cord)

In the gray matter of the spinal cord and brain, clusters of neuronal cell bodies form functional groups called...

Central canal

Small space that extends the entire length of the spinal cord and is filled with cerebrospinal fluid

intercostal or thoracic nerves.

The anterior rami of spinal nerves T2-T12 do not enter into the formation of plexuses and these nerves are known as ... These nerves directly connect to the structures they supply in the intercostal spaces.

Dermatomes

The area of the skin that provides sensory input to the CNS via one pair of spinal nerves or the trigeminal (V) nerve -The nerve supply in adjacent dermatomes overlaps somewhat. - Knowing which spinal cord segments supply each dermatome makes it possible to locate damaged regions of the spinal cord. If the skin in a particular region is stimulated but the sensation is not perceived, the nerves supplying that dermatome are probably damaged.

Tracts VS Nerves

Tracts: bundles of axons in the CNS Nerves: bundles of axons in the PNS

horns

The gray matter on each side of the spinal cord is subdivided into regions called....

endoneurium

The innermost layer - covers individual axons within a nerve, whether myelinated or unmyelinated

pia mater

The innermost meninx - a thin transparent connective tissue layer that adheres to the surface of the spinal cord and brain - consists of interlacing bundles of collagen fibers and some fine elastic fibers - Within the pia mater are many blood vessels that supply oxygen and nutrients to the spinal cord.

dura mater

The most superficial of the three spinal meninges - composed of dense, irregular connective tissue - forms a sac from the level of the foramen magnum in the occipital bone, where it is continuous with the dura mater of the brain, to the second sacral vertebra.

Reflex arc Step 2: Sensory neuron

The nerve impulses propagate from the sensory receptor along the axon of the sensory neuron to the axon terminals, which are located in the gray matter of the spinal cord or brain stem.

Epineurium

The outermost covering over the entire nerve

Reflex arc Step 5: Effector

The part of the body that responds to the motor nerve impulse, such as a muscle or gland - Its action is called a reflex

reflex arc (reflex circuit)

The pathway followed by nerve impulses that produce a reflex

Spinal cord and nerves and homeostasis

The spinal cord and spinal nerves contribute to homeostasis by providing quick, reflexive responses to many stimuli. The spinal cord is the pathway for sensory input to the brain and motor output from the brain.

anterior (ventral) white columns, (2) posterior (dorsal) white columns, and (3) lateral white columns

The white matter, like the gray matter, is organized into regions. The anterior and posterior gray horns divide the white matter on each side into three broad areas - Each column, in turn, contains distinct bundles of axons having a common origin or destination and carrying similar information.

Functions of the spinal nerves and the nerves that branch from them

They connect the CNS to sensory receptors, muscles, and glands in all parts of the body.

Patellar reflex

This reflex involves extension of the leg at the knee joint by contraction of the quadriceps femoris muscle in response to tapping the patellar ligament - This reflex is blocked by damage to the sensory or motor nerves supplying the muscle or to the integrating centers in the second, third, or fourth lumbar segments of the spinal cord. It is often absent in people with chronic diabetes mellitus or neurosyphilis, both of which cause degeneration of nerves. It is exaggerated in disease or injury involving certain motor tracts descending from the higher centers of the brain to the spinal cord.

Babinski reflex

This reflex results from gentle stroking of the lateral outer margin of the sole. - The great toe dorsiflexes, with or without a lateral fanning of the other toes. - This phenomenon normally occurs in children under 1½ years of age and is due to incomplete myelination of fibers in the corticospinal tract. - A positive Babinski sign after age 1½ is abnormal and indicates an interruption of the corticospinal tract as the result of a lesion of the tract, usually in the upper portion.

What surrounds and protects the delicate nervous tissue of the spinal cord?

Two types of connective tissue coverings: 1. bony vertebrae 2. tough, connective tissue meninge - plus a cushion of cerebrospinal fluid (produced in the brain)

spinal reflex

When integration takes place in the spinal cord gray matter, the reflex is called a ... An example is the familiar patellar reflex (knee jerk).

Stimulus

a change in the internal or external environment

anterior median fissure

a deep, wide groove on the anterior (ventral) side of the white matter of the spinal cord

plexus

a network of axons from the anterior rami of spinal nerves that do not go directly to the body structures that supply and instead form networks on both the left and right sides of the body by joining with various numbers of axons from anterior rami of adjacent nerves.

ipsilateral reflex

a reflex arc in which sensory nerve impulses enter the spinal cord on the same side from which motor nerve impulses leave it.

flexor or withdrawal reflex

a reflex involving a polysynaptic reflex arc that results when, for instance, you step on a tack. In response to such a painful stimulus, you immediately withdraw your leg - ipsilateral reflex arc - polysynaptic - reciprocal innervation

epidural space

a space between the dura mater and the wall of the vertebral cavity - contains a cushion of fat and connective tissue that protects the spinal cord

spinal cord

although roughly cylindrical, is flattened slightly in its anterior-posterior dimension - In adults, it extends from the medulla oblongata, the inferior part of the brain, to the superior border of the second lumbar vertebra - Thus, the spinal cord does not extend the entire length of the adult vertebral column.

The white matter consists primarily of

bundles of myelinated axons of neurons.

motor (descending) tracts

consist of axons that carry nerve impulses from the brain.

Sensory (ascending) tracts

consist of axons that conduct nerve impulses toward the brain.

posterior (dorsal) gray horns

contain somatic and autonomic sensory nuclei

anterior (ventral) gray horns

contain somatic motor nuclei, which provide nerve impulses for contraction of skeletal muscles.

anterior (ventral) root

contains axons of motor neurons, which conduct nerve impulses from the CNS to effector organs and cells.

posterior (dorsal) root

contains only sensory axons, which conduct nerve impulses from sensory receptors in the skin, muscles, and internal organs into the central nervous system.

lateral and anterior spinothalamic tracts

convey nerve impulses for sensing pain, warmth, coolness, itching, tickling, deep pres-sure, and a crude, poorly localized sense of touch.

The gray matter consists of

dendrites and cell bodies of neurons, unmyelinated axons, and neuroglia.

gray commissure

forms the crossbar of the H. In the center of the gray commissure is a small space called the central canal

typical spinal nerve

has two connections to the cord: a posterior root and an anterior root

somatic reflexes

involve contraction of skeletal muscles.

polysynaptic reflex arc

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

muscle stretch is followed by

muscle contraction, which relieves the stretching.

The stretch reflex operates as a feedback mechanism to control ?

muscle length by causing muscle contraction

The spinal cord has two principal functions in maintaining homeostasis

nerve impulse propagation and integration of information

tendon reflex

operates as a feedback mechanism to control muscle tension by causing muscle relaxation before muscle force becomes so great that tendons might be torn. - less sensitive than the stretch reflex, YET it can override the stretch reflex when tension is great, making you drop a very heavy weight, for example. - ipsilateral reflex arc - polysynaptic

All fascicles are wrapped in...

perineurium - the middle layer

Sensory and motor tracts of the spinal cord are continuous with ....

sensory and motor tracts of the brain.

muscle spindles

sensory receptors in the muscle

posterior median sulcus

shallower, narrow furrow on the posterior (dorsal) side of the white matter of the spinal cord.

The gray matter of the spinal cord

shaped like the letter H or a butterfly and is surrounded by white matter

Nerve impulses from sensory receptors propagate up the spinal cord to the brain along two main routes on each side

spinothalamic tracts and the posterior columns

spinal meninges

surround the spinal cord and are continuous with the cranial meninges, which encircle the brain

sensory receptors for tendon reflex

tendon (Golgi tendon) organs - lie within a tendon near its junction with a muscle

Spinal nerves

the paths of communication between the spinal cord and the nerves supplying specific regions of the body

muscle tone

the small degree of contraction present while the muscle is at rest.

meninges

three connective tissue coverings that encircle the spinal cord and brain