Lab 11: Nervous Tissue & Spinal Cord (Vocab)

Homeostasis

ability of the body to maintain a controlled and stable environment by responding to internal & external stimuli

What are the 2 major division of the nervous system?

1. Central Nervous System

2. Peripheral Nervous System

List the components and functions of the CNS

• brain

• spinal cord

• processes info received by PNS

• controls actions of all parts of body

• site for thoughts emotions & memory

List the components of the PNS

• cranial & spinal nerves

• ganglia

• sensory receptors

The nervous system consists of 2 categories of cells:

1. Neurons

2. Neuroglia

What is the function of neurons

• impulse conduction

• responsible for all special attributes associated w/ the nervous system (e.g. thinking, controlling muscle activity, regulating glands)

Neurons can be divided into 3 classes. What is each one’s function?

1. Sensory (afferent) neurons → conducts impulse from sensory receptor to CNS

2. Interneuron (association neuron) → integrated info from the sensory neurons & passes the stimulus to motor neurons

3. Motor (efferent) neurons → the neuron that conducts the impulse from the CNS to an effector, usually a muscle or a gland

Describe the structure & function of: dendrites

structure → short, tapering, branched; found on soma (cell body) of axon

function → carreis electrical signals, usually graded potentials, toward the cell body

Describe the structure & function of: cell body

structure → contains nucleus surrounded by cytoplasm

function → inegrates signals from dendrites, decides whether to send action potential

Describe the structure & function of: axon

structure → long, slender projection of a neuron

function → conducts action potentials away from the soma

Describe the structure & function of: axon hillock

structure → cone-shaped elevation where the axon joins to the cell body

function → nerve impulses arise at this junction

Describe the structure & function of: axon collateral

structure → side branches along an axon

function → (of muscle spindle sensory neurons) synapses w/ inhibitory interneuron in the integrating center; relay nerve impulses to the brain over ascending pathways

Describe the structure of: axon terminals

structure → the many fine processes that an axon & its collaterals divide into

Describe the structure & function of: synaptic end bulbs/varicosities

structure → bulb-shaped tips of axon terminals

function → secretes neurotransmitters; converts electrical impulses into chemical signsls to communicate

Describe the structure & function of: Schwann cells

structure → neuroglial cell of the PNS that encircles PNS axons

function → forms myelin sheath & neurolemma; participates in axon regeneration

Describe the structure & function of: myelin sheath

structure → multilayered lipid & protein covering around axons of many PNS & CNS neurons

function → insulates & increases speed of nerve impulse conduction

Describe the structure & function of: neurolemma

structure → outer, peripheral, nucleated cytoplasmic layer of the Schwann Cell

function → aids axon regenreation by forming a regeneration tube

Describe the structure & function of: myelin sheath gaps/nodes of ranvier

structure → space along myelinated axons between the individual Schwann cells that form the myelin sheath

function → enable rapid signal transmission via saltatory conduction

Neurons can be classified into 3 categories according to their structure:

1. Multipolar → several dendrties & one axon; dominates the CNS

2. Bipolar → one dendrite & one axon; found in retina of eye, inner ear, nasal epithelium

3. Pseudounipolar → fused axon & dendrite that emerge from the cell body as one unit; form sensory receptors in PNS

List the general functions of neuroglia

• provide structural support for neurons

• form myelin sheath

• englfing microorganisms & cell debris

• forming CSF

• prevent substances from entering CNS

List the 4 CNS neuroglia and describe each

1. Astrocytes → support neurons, maintain chemical environment & BBB

2. Oligodendrocytes → forms mylein sheath around CNS axons

3. Microglial Cells → phagocytosis; remove cellular debris, phagocytize microbes & damaged tissue

4. Ependymal Cells → cuboidal to columnar cells that possess microvilli and cilia; produce CSF, form blood-CSF barrier

List the 2 PNS neuroglia and their functons

1. Schwann cells → forms myelin sheath and neurolemma around PNS axons

2. Satellite cells → flat cells → surround cell bodies of PNS ganglia; provides structural support

Distinguish between the functions of neurons & neuroglia

1. neurons → generate/propogate nerve impulses; thinking, controling muscle activity, regulating glands

2. neuroglia → multiply/divide in mature nervous system; structural support, form myelin sheath, engulfing microorganisms/cell debris, form CSF

Describe the functions of white matter vs. gray matter of the spinal cord

white matter → carry sensory info to the brain & motor info back to PNS; myelinated; EPSPs & IPSPs

gray matter → contains cell bodies & axons of interneurons; unmyelinated; contains many sensory/motor tracts

Describe the 3 spinal meninges

1. Dura mater → superficial; thick, strong — composed of dense irregular connective tissue

2. Arachnoid mater → midde; thin, avascular — composed of collagen & elastic fibers

3. Pia mater → innermost; thin, transparent connective tissue that adheres to spinal cord; filled w/ blood vessels

Describe the 3 “spaces” of the spinal cord

1. Epidural space → space betwen spinal dura mater & vertebral canal; contains areolar CT & plexus of veins to protect spinal cord

2. Subdural space → space between dura mater & arachnoid mater that contains interstitial fluid

3. Subarachnoid space → space betwn arachnoid mater & pia mater; contains shock-absorbing CSF

List the meninges and spaces from deep to superficial

1. Pia mater

2. Subarachnoid space

3. Arachnoid mater

4. Subdural space

5. Dura mater

6. Epidural space

Describe the structure & function of: anterior horn

contains somatic motor nuclei — clusters of cell bodies of somatic motor neurons

• provides skeletal muscle contraction

Describe the structure & function of: posterior horn

• contains axons of incoming sensory neurons + cell bodies & axons of interneurons

Describe the structure & function of: central canal

• center of spinal cord → filled w/ CSF; extends entire length of spinal cord

Describe the structure & function of: anterior and posterior roots

anterior root → contain axons of motor neurons

posterior root → contain sensory axons; has spinal ganglion

Describe the structure & function of: ganglia

contains cell bodies of neurons; relay & process sensory info between CNS & PNS

Describe the structure & function of: anterior median fissure

wide groove; separates anterior portion of spinal cord into symmetrical halves

Describe the structure & function of: posterior median sulcus

narrow; separates posterior portion into halves

Describe the structure & function of: filum terminale

thin fibrous tissue that extends from conus medullaris to coccyx; anchors

What is a nerve?

bundle of axons; PNS

The anterior & posterior roots join outside the spinal cord to form ___ that have ______ functions

mixed nerves; both sensory & motor functions

After leaving the spinal column, the anterior spinal nerves divide into several branches called ___

ramiplexus

The anterior rami, except for those on the thoracic spinal nerves, often form a complex network of motor nerves called a ___ which ___ areas of the body

plexus; innervate

What are reflexes?

rapid-automatic sequences that occur in resp. to a stimulus; maintains homeostasis

List the 5 components of a reflex arc

1. Sensory receptor

2. Sensory neuron

3. Integrating center

4. Motor neuron

5. Effector

Contrast autonomic/visceral and somatic reflexes

autonomic/visceral → results in secretion by a gland/contraction of smooth or cardiac muscle; regulating functions like digestion, elimination, blood pressure, etc.

somatic → results from contraction fo skeletal muscles

Describe stretch reflexes

• spimplest form of somatic reflexes

• effector muscle is the same muscle as the one that is stimulated

What is a sensory receptor

distal end of sensory neuron (dendrite) serves as a receptor; responds to a stimulus

Where are sensory neurons located

located in gray matter

What is an integrating center

• one or more regions of gray matter within CNS

• can have monosynaptic or polysynaptic reflex arc

List 4 examples of receptors that can be involved in a reflex arc

1. baroreceptors → monitors blood pressure

2. mechanoreceptors → e.g. muscle spindles

3. thermoreceptors → temperature changes

4. tendon organs → detect changes in muscle tension caused by passive stretch or muscular contraction

List 4 examples of effectors that can be involved in a reflex arc

1. skeletal muscle

2. smooth muscle

3. cardiac muscle

4. glands

List the 4 types of somatic reflexes tested in lab

1. Achilles Tendon

2. Patellar

3. Biceps

4. Triceps

Describe the procedure, effector, & normal response of the Achilles Tendon reflex

procedure:

1. subject stands resting one knee on stool, foot hands relaxed

2. tester locates achilles tendon and uses rubber mallet to strike

effector → gastrocnemius muscle (calf)

normal response → slight plantar flexion of the foot

Describe the procedure, effector, & normal response of the Patellar Reflex

procedure:

1. subject sits on lab bench w/ both legs legs hanging freely

2. tester locates patellar tendon (inferior to patella) & softly strikes it with wide end of rubber mallet

effector → quadriceps femoris (anterior muscle of thigh)

normal response → slight extension of lower leg at the knee

Describe the procedure, effector, & normal response of the Biceps reflex

procedure:

1. facing each other, tester holds subject’s left elbow in right hand. subject’s forearm should rest on tester’s forarm — bent and relaxed

2. tester places thumb on biceps tendon in the antecubital region

3. tester strikes tip of their thumb w/ mallet

4. watch for movement of subject’s brachium, antebrachium, hand or fingers

effector → biceps brachii muscle

normal response → slight flexion of the forearm at the albow

Describe the procedure, effector, & normal response of the Triceps Reflex

procedure:

1. subject flexes their arm at the elbow

2. tester hold subjects wrist & subject relaxes arm completely, resting qweight of arm in the tester’s fingers

3. tester strikes triceps tendon, above the olecranon of the ulna

effector → triceps brachii muscle

normal response → slight extension of the forearm at the elbow

What is the one superfical/cutaneous reflex that we tested? Describe the procedure & normal and abnormal response of it.

plantar flexion

procedure:

1. subject remove right shoe/sock

2. tester takes metal handle of mallet and runs it firmly towards the big toe

normal response → in adults: toes flex

abnormal response → in adults: babinski sign — toes spread (normal in children under 18 months)

List the 3 autonomic/visceral reflexes we tested

1. Salivary

2. Pupillary

3. Diving

Describe the procedure, effector, & normal response of the Salivary reflex

procedure:

1. subject rinses mouth with water

2. tester dips cotton swab in water & places it under subject’s tongue for a few seconds.

3. subject collects all saliva produced for 3 mins in a clean graduated cylinder & measures the volume produced (not including the bubbles)

4. Subject rinses their mouth with water

5. The tester dips a new cotton swab in a glucose solution and places it under subjects tongue

6. subject collects all saliva produced for 3 mins & measures again

7. rinse mouth with water

8. Repeat with lemon juice

effector → salivary glands

normal response → immediate, involuntary increase of saliva production

Describe the procedure, effector, & normal response of the Pupillary Light reflex

procedure:

1. siubject stands facing the tester. tester notes relative size of subject’s pupils

2. tester quickly flashes panlight into subject’s eye & notes change in pupil diameter

effector → iris

normal response → both pupils get smaller with light

Describe the procedure, effector, & normal response of the Diving reflex

procedure:

1. Obtain pulse oximeter. Take resting pulse of subject

2. subject takes 3 deep breaths before bending at waist to submerge their face in the cold water

3. tester times for 30 seconds once the subect has submerged

4. recirder will monitor heart rate of the subject

effector → heart; vascular smooth muscle

normal response → heart rate drops to preserve body temperature

Why are stretch reflexes considered to be simpler than other reflexes?

• monosynaptic reflex arc — only involves sensory and motor neuron connected by a single synapse

What is the diff. between a monosynaptic & polysynaptic reflex?

monosynapotic → NO interneurons, faster ; involves only 1 synapse between sensory & motor neuron (e.g. stretch reflex)

polysynaptic → 1+ interneuron betwn sensory & motor neuron; 2+ synapses, more complex & slower (e.g. withdrawal or pain reflex)

How can the reflexes tested be used for diagnostic purposes?

Assess the integrity of the nervous system & locate lesions

All reflexes are designed to maintain homeostasis in the body — how so? Give a few examples of somatic & autonomic reflexes that help maintain homeostasis

1. Involuntary, rapid, & predictable responses to sensory stimuli allow body to detect disruptions & immediately correct internal conditions

2. Somatic → stretch reflex: causes contraction to prevent overextension, maintaining posture & joint stability

3. Autonomic → pupillary reflex: constriction of pupil in bright light and dilation in dim light protects the retina & ensures optimal vision