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Anatomy and Physiology > Functions of the Nervous System > Flashcards

Functions of the Nervous System Flashcards

1
Q

Functions of the Nervous System

A 
Sensory input (gathering information) 
o	Sensory receptors monitor changes (stimuli) internal and external

Integration
o Nervous system processes and interprets sensory input
 Decides whether action is needed

Motor Output
o A response, or effect, activates muscle or glands

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2
Q

Organisation of the Nervous System

A 
Classification is based on: 
o	Structures (structural classification) 
o	Activities (functional classification)
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3
Q

Structural Classification

A 
Central Nervous System (CNS) 
o	Organs 
-       Brain and Spinal Cord 
o	Function 
-       Integration; command center 
	Interprets incoming sensory information 
	Issues outgoing instructions

Peripheral Nervous System (PNS)
o Nerves extending from the brain and spinal cord
 Spinal Nerves (carry impulse to and from the spinal cord)
 Cranial Nerves (carry impulses to and from the brain)
o Functions
 Serve as communication lines among sensory organs, the brain and spinal cord and glands or muscles

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4
Q

Nervous Tissue: Support Cells

A
  • Support cells in the CNS are grouped together as neuroglia

General functions:
o Support
o Insulate
o Protect Neurons

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5
Q

Nervous Tissue: Principal Cell Types

A 
Composed of two principal cell types 
o	Supporting Cells 
	Resemble neurons 
	Unable to conduct nerve impulses 
	Never lose the ability to divide 
o	Neurons
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6
Q

Astrocytes

A

o Abundant, star-shaped cells
o Brace and anchor neurons to blood capillaries
o Determine permeability and exchanges between blood capillaries and neurons
o Protect neurons from harmful substances in blood
o Control the chemical environment of the brain (regulate concentration of ions and chemicals)

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7
Q

Microglia

A

o Spiderlike phagocytes
o Monitor health of nearby neurons
o Dispose of debris (dead brain cells, bacteria)

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8
Q

Ependymal Cells

A

o Line cavities of the brain and spinal cord

o Beating cilia assist with circulation of cerebrospinal fluid

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9
Q

Oligodendrocytes

A

o Wrap around nerve fibres in the CNS with processes

o Produce myelin sheaths

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10
Q

Neurons (nerve cells)

A
  • Specialised to transmit messages (nerve impulses)
  • Major regions of all neurons
    o Cell body (nucleus and metabolic center of the cell)
    o Processes (fibers that extend from the cell body)
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11
Q

Neuron: Cell Body

A

o Nucleus with large nucleolus
o Nissl Bodies = Rough Endoplasmic Reticulum
o Neurofibrils = Intermediate filaments that maintain cell shape

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12
Q

Neuron: Processes

A

Dendrites
 Conduct impulses towards the cell body
 Neurons may have hundreds of dendrites

Axons
 Conduct impulses away from the cell body
 Neurons have only one axon arising from the cell body at the axon hillock
 End in axon terminal
• Contains vesicles with neurotransmitters
• Separated form the next neuron by a gap

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13
Q

Synaptic Cleft and Synapse

A

Synaptic Cleft
 Gap between axon terminals and the next neuron

Synapse
 Functional junctional between nerves where a nerve impulse is transmitted

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14
Q

Myelin

A
  • White, fatty material covering axons
  • Protects and insulates fibers
  • Increases rate of nerve impulse transmission

Myelin Sheaths
o Oligodendrocytes
 Produce myelin sheaths around axons of the CNS
 Lack a neurilemma (cannot regenerate)

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15
Q

Neuron Terminology

A
  • Nuclei = clusters of cell bodies in the CNS
  • Ganglia = small collections of cell bodies outside the CNS in the PNS
  • Tracts = bundles of nerve fibers in the CNS
  • Nerves = bundles of nerve fibers in the PNS
  • White Matter = collections of myelinated fibers in CNS
  • Gray Matter = mostly unmyelinated fibers and cell bodies in CNS
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16
Q

Neuron Functional Classification: Sensory Neurons

A

o Carry impulses from the sensory receptors to the CNS

Receptors include:
 Cutaneous sense organs in the skin
• Pain receptors (most common, least sensitive)
 Proprioceptors in muscles and tendons
• Detect tension or degree of stetch within a skeletal muscle

o Provide information both internally and externally

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17
Q

Neuron Functional Classification: Motor Neurons

A

o Carry impulses from the CNS to viscera and/or muscles and glands
o Cell bodies are found within the CNS

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18
Q

Neuron Functional Classification: Interneurons

A

o Cell bodies located in the CNS

o Connect sensory and motor neurons in neural pathways

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19
Q

Neuron Structural Classification: Multipolar Neurons

A

o Many extensions from the cell
o All motor and interneurons are multipolar
o Most common structural types

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20
Q

Neuron Structural Classification: Bipolar Neurons

A

o One axon and one dendrite
o Located in special sense organs (e.g., nose and eye)
o Rare in adults

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21
Q

Neuron Structural Classification: Unipolar Neurons

A

o Have a short single process leaving the cell body
o Sensory neurons found in PNS ganglia
o Conduct impulses both towards and away from the cell body
o Only small processes at the end are considered dendrites = remainder is considered the peripheral process and central process

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22
Q

Functional Properties of Neurons

A

Irritability
o Ability to respond to a stimulus and convert it to a nerve impulse

Conductivity
o Ability to transmit the impulse to other neurons, muscles or glands

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23
Q

The Nerve Impulse: Resting Membrane Potential

A

Plasma membrane at rest is inactive (polarised)
 Fewer positive ions are inside the neuron’s plasma membrane than outside
• Potassium is the major positive ion inside the cell
• Sodium is the major positive ion outside the cell

If inside the membrane is more negative than the outside, the cell remains inactive

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24
Q

The Nerve Impulse: Local Depolarisation

A

o A stimulus changes the permeability of the neuron’s membrane to sodium ions
o Sodium channels now open, and sodium diffuses into the neuron
o Inward rush of sodium ions changes the polarity at that site and is called depolarisation
 Graded Potential (localised depolarisation) exists if inside of membrane is more positive

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25
Q

The Nerve Impulse: Depolarisation and Generation of Action Potential

A

If stimulus is strong enough and sodium influx is great enough
 Local depolarisation activates the neuron to conduct an action potential (nerve impulse)

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26
Q

The Nerve Impulse: Propagation of an Action Potential

A

o If enough sodium enters the cell, the action potential starts and is propagated over the entire axon
o All or none response
 Nerve impulse either is propagated along entirety of fibre or not at all

o Fibers with myelin sheaths conduct nerve impulses more quickly

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27
Q

The Nerve Impulse: Repolarisation

A

o Membrane permeability changes again
 Becomes impermeable to sodium ions and permeable to potassium ions

o Potassium ions rapidly diffuse out of the neuron
 Repolarising the membrane

o Involves restoring the inside of the membrane to a negative charge and the outer surface to a positive charge

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28
Q

The Nerve Impulse: Initial Ionic Conditions are Restored

A

With sodium-potassium pump
 With the use of ATP
• Three sodium ions are ejected from the cell
• Two potassium ions are returned to the cell

Until repolarisation is complete
 A neuron cannot conduct another nerve impulse

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29
Q

The Nerve Impulse: Steps

A

1) Resting Membrane Potential is Polarised
2) Stimulus Initiates Local Depolarisation
3) Depolarisation and Generation of an Action Potential
4) Propagation of an Action Potential
5) Repolarisation
6) Initial Ionic Conditions of Sodium and Potassium are Restored

30
Q

Condition within Neuron Covered in a Myelin Sheath

A
  • Send nerve impulses rapidly
  • Nerve impulses ‘jumps’ from node to node along the length of fiber
    o No electrical current can flow through axon membrane with fatty, myelin insulation
  • Process is known as Saltatory Propagation
31
Q

Transmission of the Signal at Synapses

A

Step 1:
o Action potential reaches the axon terminal  electric charge opens calcium channels

Step 2:
o Calcium causes vesicles containing the neurotransmitter chemical to fuse with the axonal membrane

Step 3:
o Entry of calcium into the axon terminal causes pore like openings to form
 Releasing the neurotransmitter into the synaptic cleft

Step 4:
o Neurotransmitter molecules diffuse across the synaptic cleft
 Bind to receptors on the membrane of the next neuron

Step 5:
o If enough neurotransmitter is released  sodium ions move into the cell -> graded potential is generated
 Eventually an action potential will occur in the neuron beyond the synapse

Step 6:
o Electrical changes prompted by neurotransmitter bindings are brief
 Neurotransmitter is quickly removed from the synapse either by reuptake or by enzymatic activity -> sodium ions are then pumped out of the cell v
 Transmission of an impulse is electrochemical
• Transmission down neuron = electrical
• Transmission to next neuron = chemical

32
Q

Nervous Tissues: Reflexes

A
  • Reflexes are rapid, predictable, and involuntary responses to stimuli
  • Occur over neural pathways called reflex arcs

Two types of reflexes
o Somatic Reflexes
o Autonomic Reflexes

33
Q

Somatic Reflexes

A
  • Reflexes that stimulate the skeletal muscles
  • Involuntary (although skeletal muscle is normally under voluntary control)
  • Example: pulling you hand away from a hot object
34
Q

Autonomic Reflexes

A
  • Regulate the activity of smooth muscles, the heart, and glands
  • Example: Regulation of smooth muscles, heart and blood pressure, glands, digestive system
35
Q

Five Elements of a Reflex Arc

A
  1. Sensory Receptor reacts to a stimulus
  2. Sensory Neuron carries message to the integration center (CNS)
  3. Integration Center (CNS) (interneurons process information and direct motor output)
  4. Motor Neuron carries messages to an effector
  5. Effector Organ (muscle or gland to be stimulated)
36
Q

Two-Neuron Reflex Arc

A
  • Simplest type

Example: patellar (knee-jerk) reflex
o Tapping Patella stimulates stretch receptors
o Signals are then relayed along a sensory neuron to the spinal cord
o Motor neuron sends signal to effector

37
Q

Three-Neuron Reflex Arc

A

Consists of five elements:
o Receptor, sensory neuron (carries information to spinal cord), interneuron (process information), motor neuron (carries information to effector), effector

Example: flexor (withdrawal) reflex
- Does not require input from the brain  spinal cord does not receive signal from sensory receptor

38
Q

Brain Regions

A

o Cerebral hemispheres (cerebrum)
o Diencephalon
o Brain stem
o Cerebellum

39
Q

Functional Anatomy of the Brain

A

Cerebral hemispheres are paired superior parts of the brain
o Include more than half of the brain mass
o Surface is made of ridges (gyri) and shallows grooves (sulci)
o Fissures are deeper grooves
- Two hemispheres are separated by the Longitudinal fissure
o Lobes are named for the cranial bones that lie over them

40
Q

Main Regions of the Cerebral Hemispheres

A
  • Cortex (superficial gray matter)
  • White Matter
  • Basal nuclei (deep pockets of gray matter within the white matter)
41
Q

Cerebral Cortex: Primary Somatic Sensory Area

A

o Located in parietal lobe posterior to central sulcus

o Receives impulses from the body’s sensory receptors
 Pain, temperature, light tough (except for special senses)

o Sensory homunculus is a spatial map
o Left side of the primary somatic sensory area receives impulses from right side

42
Q

Cerebral Cortex: Primary Motor Area

A

o Located anterior to the central sulcus in the frontal lobe
o Allows us to consciously move skeletal muscles
o Motor neurons form pyramidal (corticospinal) tract, which descends to spinal cord
o Motor Homunculus is a spatial map

43
Q

Cerebral Areas involved in Spacial Senses

A

o Visual Area (occipital lobe)
o Auditory Area (temporal lobe)
o Olfactory Area (temporal lobe)

44
Q

Broca’s Area (Motor Speech Area)

A

o Involved in our ability to speak

o Usually in left hemisphere at the base of the central gyrus

45
Q

Cerebral Cortex: Other Specialised Areas

A

Anterior Association Area (frontal lobe)

  • Working memory and judgement
  • Problem Solving
  • Language Comprehension

o Posterior Association Area (posterior cortex)

o Speech Area (for sounding out words)

46
Q

Cerebral White Matter

A

Composed of fiber tracts deep to the gray matter
o Corpus callosum connects hemispheres
- Allows hemispheres to communicate with one another

o Tracts are known as commissures
o Association fiber tracts connect areas within a hemisphere
o Projection fiber tracts connect the cerebrum with lower CSN centers (e.g., brainstem)

47
Q

Basal Nuclei

A
  • ‘Islands’ of gray matter buried deep within the white matter of the cerebrum
  • Regulate voluntary motor activities by modifying instructions sent to skeletal muscles by the primary motor cortex

o If issues arise in this area:
 People may not be able to walk normally
 May not be able to out voluntary movements normally
 E.g., Parkinson’s Disease

48
Q

Diencephalon

A
  • Sits on top of the brain stem
  • Enclosed by the cerebral hemispheres

Made of three structures
o Thalamus
o Hypothalamus
o Epithalamus

49
Q

Thalamus

A
  • Encloses the third ventricle
  • Relay station for sensory impulses passing upward to the cerebral cortex
  • Transfers impulses to the correct part of the cortex for localisation and interpretation
    o Neurons perform the localisation and interpretation
50
Q

Hypothalamus

A
  • Makes up the floor of the diencephalon
  • Important ANS center
    o Regulate body temperature, water balance, metabolism
  • Houses the limbic center for emotions
    o Contains thirst, pain, sex, pleasure centres
  • Regulates the nearby pituitary gland
  • Houses mammillary bodies of olfaction (smell)
51
Q

Epithalamus

A
  • Forms the roof of the third ventricle
  • Houses the pineal body (an endocrine gland)
  • Includes the choroid plexus of the third ventricle (forms cerebrospinal fluid)
52
Q

Brain Stem

A
  • Attaches to the spinal cord
  • Provides a pathway for ascending and descending tracts

Parts of the brain stem
o Midbrain
o Pons
o Medulla Oblongata

53
Q

Midbrain

A
  • Extends from the mammillary bodies to the pons inferiorly
  • Cerebral aqueduct (tiny canal) connects the third and fourth ventricles
  • Two bulging fiber tracts (cerebral peduncles) covey ascending and descending impulses
  • Four rounded protrusions (corpora quadrigemina)
    o Visual and auditory reflex centers
54
Q

Pons

A
  • The rounded structure protruding just below the midbrain
  • Mostly composed of fiber tracts
  • Includes nuclei involved in the control of breathing
55
Q

Medulla Oblongata

A
  • Inferior part of brain stem -> merges into the spinal cord
  • Includes important fiber tracts
  • Contains important centers that control
    o HR, BP, breathing, swallowing, vomiting
  • Fourth Ventricle -> posterior to pons and medulla
  • Motor fibers cross to the other side
56
Q

Reticular Formation

A
  • Diffuse mass of gray matter along the brain stem
  • Involved in motor control of visceral organs (e.g., smooth muscle in digestive tract)

Reticular Activating System (RAS)
o Plays a role in awake/sleep cycles and consciousness
o Filter for incoming sensory information

  • Damage can result in unconsciousness or a coma
57
Q

Cerebellum

A
  • Two hemispheres with convoluted surfaces
  • Outer cortex of grey matter and inner region of white matter
  • Control balance
  • Provides precise timing for skeletal muscle activity and coordination of body movements
  • Fibers reach cerebellum via the equilibrium apparatus of the inner ear, eye, muscles and tendons etc.

When needed
o Send signals to ensure smooth and coordinated movement

If damaged
o Movement becomes uncoordinated (ataxia)

58
Q

Protections of the CNS

A
  • Meninges (CT membranes)
  • Cerebrospinal Fluid (CSF)
  • Blood-brain Barrier
59
Q

Meninges: Dura Mater

A

o Outermost leathery layer
o Double-layered external covering
- Periosteum (attached to inner surface of the skull)
- Meningeal Layer (outer covering of the brain)

o Folds inward in several areas

  • Falx cerebri
  • Tentorium cerebelli
60
Q

Meninges: Arachnoid Mater

A

o Middle layer
o Weblike extensions span the subarachnoid space to attach it to the pia mater
o Subarachnoid space is filled with CSF
o Arachnoid granulations protrude through the dura mater and absorb CSF into venous blood

61
Q

Meninges: Pia Mater

A

o Internal layer

o Clings to the surface of the brain and spinal cord

62
Q

Cerebrospinal Fluid

A
  • Similar to blood plasma in composition
  • Formed continually by the choroid plexuses
    o Choroid Plexuses (capillaries in the ventricles of the brain)
  • CSF forms a watery cushion to protect the brain and spinal cord
  • Circulated in the arachnoid space, ventricles and central canal of the spinal cord
  • Forms and drains at a constant rate
63
Q

CSF Circulation

A

Step 1
o CSF is produced by the choroid plexus of each ventricle

Step 2
o CSF flows through the ventricles and into the subarachnoid space via the median and lateral apertures
o Some CSF flows through the central canal of the spinal cord

Step 3
o CSF flows through the subarachnoid space

Step 4
o CSF is absorbed into the Dural venous sinuses via the arachnoid villi

64
Q

Blood-Brain Barrier

A
  • Includes the least permeable capillaries of the body
  • Allows water, glucose and amino acids to pass through capillary walls
  • Excludes many potentially harmful substances from entering the brain such as wastes (urea, toxins(
  • Useless as a barrier against some substances (fats, respiratory gases, soluble molecules)
    o Why blood-borne alcohol and nicotine affect the brain
65
Q

Traumatic Brain Injuries

A

Concussion
o Slight brain injury (dizzy, may lose consciousness)
o Typically, little permanent brain damage occurs

Contusion
o Marked nervous tissue destruction occurs
o Coma may occur (could last hours -> lifetime)
 Due to damage of the reticular activating system

Death may occur after head blows due to:
o Intracranial Haemorrhage
 Bleeding from ruptured blood vessels

o Cerebral edema
 Swelling in the brain due to inflammatory responses to injury

66
Q

Cerebrovascular Accident or Stroke

A
  • Results when blood circulation to a brain area is blocked (by clot or ruptured blood vessel) and brain tissue dies
Loss of some functions or death may result 
o	Hemiplegia (one-sided paralysis) 
o	Aphasia (damage to speech center in left hemisphere)
67
Q

Transient Ischemic Attack

A
  • Temporary brain ischemia (restriction of blood flow)
    o Last 5 – 50 minutes
  • Numbness, temporary paralysis, impaired speech
68
Q

Spinal Cord

A
  • Extends from the foramen magnum of the skull to the first or second lumbar vertebra
  • Cauda equina is a collection of spinal nerves at the inferior end
  • Provides a two-way conduction pathway to and from the brain
  • 31 pairs of spinal nerves arise from the spinal cord
  • Major reflex center
  • Spinal reflexes are completed at this level
69
Q

Gray Matter of the Spinal Cord and Spinal Roots

A

Internal gray matter is mostly cell bodies

Dorsal horns house interneurons
o Receive information from sensory neurons in the dorsal root
o Cell bodies housed in dorsal root ganglion

Anterior horns house motor neurons of the somatic (voluntary) nervous system
o Send information out ventral root

Gray matter surrounds the central canal
o Filled with CSF

Dorsal and ventral root fuse to form the spinal nerves

70
Q

White Matter of the Spinal Cord

A
  • Composed of myelinated fiber tracts

Three regions: dorsal, lateral, ventral columns
Dorsal
 Ascending Tracts (carry sensory input to the brain)

Lateral and Ventral
 Ascending and Descending Tracts

  • Sensory (afferent) tracts conduct impulses toward brain
  • Motor (efferent) tracts carry impulses from brain to skeletal muscles

Anatomy and Physiology (14 decks)

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