1
Q
what is the function of the nervous system?
A
- receives sensory information
- integrates the sensory information
- initiates reactive measures
2
Q
what do the many functions of the nervous system revolve around?
A
maintenance of homeostasis
3
Q
what is homeostasis?
A
the ability of the body to maintain a controlled and stable internal environment by responding to internal and external stimuli
4
Q
why is maintaining homeostasis important?
A
the majority of body functions can only occur if conditions such as:
- temp.
- pH
- solute concentrations
are maintained within specific physiological parameters
5
Q
what are the two structural divisions of the nervous system?
A
- CNS: central nervous system
- PNS: peripheral nervous system
6
Q
what constitutes the central nervous system?
A
- brain
- spinal cord
7
Q
what constitutes the peripheral nervous system?
A
- cranial nerves
- spinal nerves
- ganglia
- sensory receptors
8
Q
what does the central nervous system do?
A
- processes the information received by sensory receptors of the PNS
- controls actions of all parts of the body
- site of thoughts, emotions, memory
9
Q
what are neurons?
A
cells that form the functional portion of the nervous system
- highly specialized for impulse conduction, possess electrical excitability
- responsible for all special attributes associated w/ nervous system (thinking, controlling muscles, regulating glands)
- cannot divide
10
Q
what are the three classes of neurons based on function?
A
- sensory neurons
- interneurons
- motor neurons
11
Q
what are sensory neurons?
A
afferent neurons that conducts impulse from sensory receptors to the CNS
12
Q
what are interneurons?
A
association neurons that integrate information from sensory neurons and passes stimuli to motor neurons
13
Q
what are motor neurons?
A
efferent neurons that conducts impulses from the CNS to an effector (muscle or gland)
14
Q
what are dendrites?
A
processes found on neurons that receive signals from other neurons and carries them to cell body
- plasma membrane contains receptor sites for binding neurotransmitters from other neurons = dendritic spines
- cytoplasm has Nissl bodies, mitochondria, etc.
15
Q
what are cell bodies?
A
main portion of neuron that contains nucleus surrounded by cytoplasm w/ organelles suspended in the cytosol
- has Nissl bodies, mitochondria, and other organelles that allow for protein synthesis
- cytoskeleton has neurofibrils (made from intermediate filaments) and microtubules
16
Q
what is the axon hillock?
A
cone-shaped elevation where axon joins to the cell body
17
Q
what is the axon collateral?
A
branchpoints along an axon’s length, usually at a right angle to the axon
18
Q
what is an axon terminal?
A
processes at the ends of axons where synaptic vesicles undergo exocytosis to release neurotransmitters
19
Q
what are synaptic end bulbs and varicosities?
A
bulb-shaped, or swollen bumps found at tips of axon terminals that contain synaptic vesicles with neurotransmitters inside
20
Q
what are Schwann cells?
A
neuroglia in PNS that can myelinate one axon or enclose ~20 unmyelinated axons
- participates in axon’s regeneration
21
Q
what is a myelin sheath?
A
multilayered lipid+protein covering around axons that:
- decreases capacitance (ability to retain charge) of the axolemma
- insulates axons
- increases speed of nerve impulse conduction
22
Q
what is the neurolemma?
A
other, nucleated cytoplasmic layer of Schwann cell
- found only in axons of PNS
- forms regeneration tube that stimulates/guides axonal growth
23
Q
what are myelin sheath gaps/Nodes of Ranvier?
A
space along myelinated axons btwn. Schwann cells
24
Q
What are the three classes of neurons according to their structure?
A
- multipolar neurons
- bipolar neurons
- pseudounipolar neurons
25
what are multipolar neurons?
neurons that have several dendrites and one axon
- dominates the CNS
26
what are bipolar neurons
neurons w/ one dendrite and one axon
- found in retinas, inner ears, nasal epithelium
27
what are pseudounipolar neurons?
neurons w/ fused axon and dendrite that emerge from cell body as one process
- dendrites of these neurons form many of the sensory receptors of the PNS
28
what are neuroglia?
cells in nervous tissue that:
- provide structural support for neurons and protects them
- form myelin sheaths around axons
- engulfs microorganisms and cell debris
- forms CSF
- prevents some substances from entering CNS
- can divide
- maintains interstitial fluid of nervous tissue
29
what are astrocytes?
CNS neuroglia
- star-shaped
- largest, most numerous neuroglia
- Protoplasmic/Fibrous astrocytes
- supports neurons w/ its processes
- forms blood-brain barrier
- regulates growth in embryo
- help maintain appropriate chemical environment
- influences formation of neural synapses
30
what are oligodendrocytes?
CNS neuroglia
- smaller than astrocytes w/ fewer processes
- forms and maintains myelin sheath around CNS axons
31
what are microglia?
CNS neuroglia
- small, w/ slender processes
- function as phagocytes
- remove cellular debris
- phagocytize microbes and damaged tissue
32
what are ependymal cells?
CNS neuroglia
- cuboidal to columnar shaped
- arranged in single layer
- has both microvilli and cilia
- lines brain's ventricles and spinal cord's central canal as well as subarachnoid space
- produces CSF
- maintains the blood-cerebrospinal fluid barrier
33
what are schwann cells?
PNS neuroglia
- can myelinate one axon
- can enclose ~20 unmyelinated axons
- participates in regeneration of axons
34
what are satellite cells?
PNS neuroglia
- flat, surrounds cell bodies of PNS in ganglia
- provides structural support to the cell bodies
- regulates exchange of materials btwn cell bodies and interstitial fluid around them
35
what protects the spinal cord?
- bony vertebral column
- meninges
- CSF
36
what is the length of the spinal cord?
extends from medulla oblongata to L2 vertebrae
37
what is white matter in SC?
bundles of myelinated axons (ganglia) that make up white matter in SC carry sensory info to the brain and motor info back to the PNS
38
what is grey matter in SC?
contains cell bodies and axons of interneurons
39
what are spinal meninges?
three layers of connective tissue that surround the spinal cord, continuous w/ the cranial meninges that enclose the brain
40
what is the function of the spinal meninges?
- protects and cushions the spinal cord in the vertebral column
41
what is the dura mater?
- most superficial of the meninges
- composed of dense, irregular CT
- toughest, most protective layer of the meninges
42
what is the arachnoid mater?
- intermediate layer of the meninges
- composed of collagen and elastin fibres
- weblike structure
43
what is the pia mater?
- most deep layer of the spinal meninges
- squamous to cuboidal cells w/ interlacing bundles of collagen and elastin fibres
- adheres to the spinal cord
- highly vascular to nourish the tissues of the spinal cord
- has denticulate ligaments
44
what is the epidural space?
space btwn dura mater and vertebral column
- filled w/ fat + CT
45
what is the subdural space?
space btwn arachnoid mater and dura mater
- filled w/ interstitial fluid
46
what is the subarachnoid space?
space btwn arachnoid mater and pia mater
- filled w/ cerebrospinal fluid
47
what is the anterior grey horn of the spinal cord?
contains **somatic motor** nuclei, cell body clusters of somatic neurons that provide nerve impulses for skeletal muscle contraction
48
what is the posterior grey horn of the spinal cord?
contains axons of incoming **sensory** neurons and cell bodies and axons of interneurons
49
what are spinal nerves?
- collection of nerves originating from spinal cord's posterior and anterior roots
- path of communication between spinal cord and the rest of the body
- 31 pairs
50
what is the central canal?
- hole in center of grey commissure
- extends entire length of the spinal cord
- filled w/ cerebrospinal fluid
51
what are nerve roots?
axon bundles that connect each spinal nerve to a segment of the spinal cord
52
what are anterior roots?
axon bundles of **motor** neurons
- conducts nerve impulses from central nervous system to effectors
53
what are posterior roots?
axon bundles of **sensory** neurons
- conducts nerve impulses from sensory receptors to the central nervous system
54
what are ganglia?
cell body bundles of axons
55
what is the anterior median fissure?
wide groove on anterior side of spinal cord, penetrates white matter of spinal cord and divides it into left/right
56
what is the posterior median sulcus?
narrow furrow on posterior side of spinal cord, penetrates white matter of spinal cord and divides it into left/right
57
what is the filum terminale?
most inferior extension of the pia mater that anchors spinal cord to coccyx
58
where do the spinal nerves exit the spinal column?
spinal nerve pass through the intervertebral foramina to exit spinal column
59
what is a nerve?
bundle of axons from multiple neurons
- part of PNS
60
what are the two distinct roots that the spinal nerves form as they emerge from the spinal cord?
- anterior root
- posterior root
61
what are mixed nerves?
nerves that have both sensory and motor functions
- result of anterior and posterior roots joining outside the spinal cord
62
what are rami?
branches that the spinal nerves divide into after leaving the spinal column
63
what are plexuses?
complex, weblike network of motor nerves that the anterior rami often form into
- contains axons from neighbouring spinal nerves
- innervates specific areas of the body
64
what are reflexes?
rapid, automatic sequences of actions that occur in response to a stimulus
ex. Babinski sign during plantar reflex, flexion during bicep reflex
65
what is the function of reflexes?
to maintain homeostasis in the body
66
what is a reflex arc?
the route an impulse takes to produce a reflex action
67
what are the basic components of a reflex arc?
1. sensory receptor
2. sensory neuron
3. integrating centre
4. motor neuron
5. effector
68
describe the path a reflex arc takes
1. info received by sensory receptor transmitted to sensory neuron
2. sensory neuron sends sensory info to an integrating centre (SC in spinal reflexes)
3. info processed by interneurons
4. interneurons transfer info to motor neurons
5. motor neurons transmit impulse to an effector (muscle or gland)
69
what are autonomic/visceral reflexes?
reflex that results in unconscious, involuntary secretion by a gland or contraction of smooth/cardiac muscle
70
what is the function of autonomic/visceral reflexes?
they regulate body functions such as digestion, elimination, blood pressure, salivation, and sweating
71
what are somatic reflexes?
type of reflexes which result in contraction of skeletal muscles
72
what is stretch reflex?
- simplest form of somatic reflexes
- effector muscle is same muscle as the one being stimulated
- prevents overstretching of muscle, controls muscle length
- constantly activated in body to maintain posture
73
what are other types of somatic reflexes?
- stretch reflex
- tendon reflex
- flexor (withdrawal reflex)
- crossed extensor reflex
74
what is a receptor?
responds to stimulus by producing graded potentials (generator potentials)
- usually distal ends of sensory neuron dendrites or an associated sensory structure
ex. pain receptors, thermoreceptors, chemoreceptors
75
what is an integrating centre?
1 or more regions in CNS that relay impulses from sensory to motor neurons
ex. medulla oblongata, spinal cord, brain
76
what are the different classes of reflex arcs based on how many synapses are found?
- monosynaptic reflex arc
- polysynaptic reflex arc
77
what is an effector?
body part that responds to motor nerve impulses
- a reflex is an action/response made by an effector
ex. organs, glands, muscles, blood vessels
78
why are reflex tests used?
they can be used as diagnostic tools to evaluate the functioning of the CNS and PNS in patients
- if reflex doesn't work normally, damage somewhere along a particular conduction pathway is suspected or nerves are missing
79
what are some examples of how abnormal responses can differ from a reflex test's normal response?
- each reflex test has normal and abnormal response, abnormal response could be:
1. exaggeration of normal response
2. minimal normal response
3. absence of a response
4. a different response altogether
80
Achilles Tendon Reflex
1. subject should stand resting one knee on a lab stool, allowing their foot to hang relaxed
2. tester locates **achilles tendon** on back of ankle, and using long side of rubber mallet, softly strike achilles tendon
3. observe any movement of foot
81
Patellar Reflex
1. subject sit on lab bench with both legs hanging freely
2. tester locates patellar tendon, softly striking it w/ wide end of rubber mallet
3. observe any movement of leg
82
Biceps Reflex
1. tester holds subject's left elbow in right hand, subject's forearm rests on tester's forearm, so subject's arm is bend and relaxed
2. tester places their thumb on biceps tendon in antecubital region
3. tester strikes tip of their thumb w/ mallet
4. watch for movement of subject's brachium, antebrachium, hand, or fingers
83
Triceps Reflex
1. subject flexes their arm at the elbow
2. tester should hold subject's wrist and subject relaxes their arm completely, resting weight of their arm in tester's fingers
3. tester strikes triceps tendon, just above olecranon of ulna
4. observe any movement in arm
84
Plantar Flexion Reflex
1. subject removes right shoe and sock
2. tester takes blunt end of mallet and runs it firmly from heel, along outer edge of the sole of the foot and across the ball of the foot towards the big toe
3. observe any movement in the toes
85
Salivary Reflex
1. subject rinses their mouth w/ drinking water
_WATER_
2. tester dips cotton swab in water and place it under subject's tongue for a few seconds, disposing swab by placing it back in paper package and putting it in the garbage
3. subject should collect all saliva produced for 3 min in a clean graduated cylinder, measuring volume produced and disposing saliva in sink and rinsing graduated cylinder
4. subject rinses their mouth w/ water
5. repeat #2 - #4. for glucose soln. and lemon juice
6. Wash graduated cylinder w/ soap and test tube brush after each subject
86
Pupillary Light Reflex
1. subject stands facing the tester, tester notes the relative size of subject's pupils
2. tester quickly flashes penlight into subject's eye and note changes in pupil diameter
87
Diving Reflex
1. obtain pulse oximeter and take resting pulse
2. subject takes 3 deep breaths before bending at waste to submerge face in cold water
3. tester starts timing for 30s once subject placed face in water
4. recorder will monitor heart rate of subject and note any changes
5. At 30s, tester taps subject on shoulder to end testing period
88
what is the effector for the achilles reflex?
gastrocnemius and soleus
89
what is the normal response for achilles reflex?
slight plantar flexion of the foot
90
what is the effector of the patellar reflex?
quadriceps femoris
91
what is the normal response of the patellar reflex?
slight extension of the lower leg at the knee
92
what is the effector of the biceps reflex?
biceps brachii
93
what is the normal response of the biceps reflex?
slight flexion of the forearm at the elbow
94
what is the effector of the triceps reflex?
triceps brachii
95
what is the normal response of the triceps reflex?
slight extension of the forearm at the elbow
96
what is the effector of the plantar flexion reflex?
gastrocnemius
97
what is the normal response in adults of the plantar flexion reflex?
all toes flex (curl)
98
what is the normal response in babies (children <18mos) of the plantar flexion reflex?
Babinski sign: toes spread/fan, great toe extends
(abnormal in adults
99
what is the effector of the salivary reflex?
salivary glands
100
what is the normal response of the salivary reflex?
production and release of saliva
101
what is the effector of the pupillary light reflex?
smooth muscle of the iris
102
what is the normal response of the pupillary light reflex?
constriction of the iris
103
what is the effector of the diving reflex?
cardiac muscle
104
what is the normal response of the diving reflex?
bradycardia
105
why are stretch reflexes considered to be simpler than other types of reflexes?
they are monosynaptic, ipsilateral reflexes
only 2 neurons and 1 synapse involved
106
what is a monosynaptic reflex arc?
reflex pathway involving 2 neurons and 1 synapse in the CNS
107
what is a polysynaptic reflex arc?
reflex pathway involving more than 2 neurons and more than 1 CNS synapse
108
what are some examples of reflexes that help maintain homeostasis?
- withdrawal reflex moves one away from pain
109
describe the grading of response for reflex tests
0 - Absent
1 - Decreased but present
2- Normal
3 - Brisk and excessive
4 - with clonus (abnormal reflex response that involves involuntary and rhythmic muscle contractions)
110
why might a crossed adductor response occur?
crossed adductor contraction occurred b/c increased right leg tone which resulted in reflex contraction of the adductor magnus w/ very slight stretch of this muscle caused by tapping the opposite knee
*see motor_ab_09.mov*
