Week 7 - Nervous System Flashcards
define the three specific functions of the nervous system
- sensory input - gathering information
- sensory receptors monitor changes, called “stimuli” occurring inside and outside the body - integration
- nervous system processes and interprets sensory input and decides whether action is needed - motor output
- a response, or effect, activates muscles or glands
describe the organization of the nervous system, including the structural and functional classifications
- structure (structural classification)
- activities (functional classification)
what is the central nervous system (CNS)?
Organs
- brain
- spinal cord
what are the functions of the central nervous system (CNS)?
- integration; command center
- interprets incoming sensory information
- issues outgoing instructions
what is the peripheral nervous system (PNS)?
- nerves extending from the brain and spinal cord
- spinal nerves: carry impulses to an from the spinal cord
- cranial nerves: carry impulses to and from the brain
what are the functions of the peripheral nervous system (PNS)?
serves as communication lines among sensory organs, the brain and spinal cord, and glands or muscles
what are the functional classifications?
- sensory (afferent) division
- motor (efferent) division
what is the sensory (afferent) division?
nerve fibers that carry information to the central nervous system
- somatic sensory (afferent) fibers carry information from the skin, skeletal muscles, and joints
- visceral sensory (afferent) fibers carry information from visceral organs
what is the motor (efferent) division?
nerve fibers that carry impulses away from the central nervous system organs to effector organs (muscles and glands)
what are the two subdivisions of the motor (efferent) division?
somatic nervous system = voluntary
- consciously (voluntarily) controls skeletal muscles
autonomic nervous system = involuntary
- automatically controls smooth and cardiac muscles and glands
- further divided into the sympathetic and parasympathetic nervous systems
what are the basic structures and functions of neuroglia types?
- support cells in the CNS are grouped together as neuroglia
general functions:
- support
- insulate
- protect neurons
what are the two principal cells types that the nervous tissue is made of? (structure and function)
1) supporting cells (called “neuroglia, “glial cells” “glia”)
- resemble neurons
- unable to conduct nerve impulses
- never lose the ability to divide
2) neurons
Describe the CNS glial cells: astrocytes
- abundant, star-shaped cells
- brace and anchor neurons to blood capillaries
- determine permeability and exchanges between blood and capillaries and neurons
- protects neurons from harmful substances in the blood
- control the chemical environment of the brain
Describe CNS glial cells: microglia
- spiderlike phagocytes
- monitor health of nearby neurons
- dispose of debris
describe CNS glial cells: ependymal cells
- line cavities of the brain and spinal cord
- cilia assist with circulation of cerebrospinal fluid
describe CNS glial cells: oligodendrocytes
- wrap around nerve fibers in the central nervous system
- produce myelin sheaths
What are the PNS glial cells?
Schwann cells
- form myelin sheath around nerve fibers in the PNS
Satellite cells
- protect and cushion neuron cell bodies
what are neurons?
- neurons = nerve cells
- cells specialized to transmit messages (nerve impulses)
what are the major regions of all neurons?
cell body - nucleus and metabolic center of the cell
processes - fibers that extend from the cell body
what is the cell body of the neuron?
- cell body is the metabolic center of the neuron
- nucleus with lark nucleolus
- nissl bodies: rough endoplasmic reticulum
- neurofibrils: intermediate filments that maintain cell shape
what are the processes (fibers)?
dendrites: conduct impulses toward 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 terminals, which contain vesicles with neurotransmitters
- axon terminals are separated from the next neuron by a gap
synaptic cleft: gap between axon terminals and the next neuron
synapse: functional junction between nerves where a nerve impulse is transmitted
describe myelin
- white, fatty material covering axons
- protects and insulates fibers
- speeds nerve impulse transmission
describe myelin sheaths
1) schwann cells - wrap axons in a jelly roll-like fasion (PNS) to form the myelin sheath
- neurilemma - part of the Schwann cecll external to the myelin sheath
- nodes of Ranvier - gaps in myelin sheath along the axon
2) Oligodendrocytes - produce myelin sheaths around axons of the CNS
- lack a neurilemma
Functional Classification - Describe Sensory (afferent) neurons
- carry impulses from the sensory receptors to the CNS
receptors: - cutaneous sense organs (skin)
- proprioceptors (muscles and tendons)
Functional Classification - Describe Motor (efferent) neurons
carry impulses from the central nervous system to viscera and/or muscles and glands
Functional Classification - Describe Interneurons (association neurons)
- cell bodies located in the CNS
- connect sensory and motor neurons
What is structural classification?
based on number of processes extending from the cell body
Describe structural classification - Multipolar Neurons
many extensions from the cell body
- all motor and interneurons are multipolar
- most common structural type
Describe structural classification - Bipolar neurons
one axon and one dendrite
- located: special sense organs (nose and eyes)
- rare in adults
Describe structural classification - Unipolar neurons
have a short single process leaving the cell body
- sensory neurons found in PNS ganglia
- conduct impulses both toward AND away from the cell body
what are the functional properties of neurons?
1) irritability
- ability to respond to a stimulus and convert it to a nerve impulse
2) conductivity
- ability to transmit the impulse to other neurons, muscles, or glands
what are the types of sensory receptors?
1) free nerve endings (pain and temperature receptors)
2) Meissner’s corpuscle (touch receptor)
3) Lamellar corpuscle (deep pressure receptor)
4) Golgi tendon organ (proprioceptor)
5) Muscle spindle (proprioceptor)
What is the electrical conditions of a resting neuron’s membrane?
- the plasma membrane at rest is inactive (polarized)
- fewer positive ions are inside the neuron’s plasma membrane than outside
- —- K is the major positive ion inside the cell
- —- Na is the major positive ion outside the cell
- as long as the inside of the membrane is negative (fewer positive ions) than the outside, the cell remains inactive
What are the steps of the nerve impulse?
- resting membrane is polarized
- stimulus initiates local depolarization
- depolarization and generation of an action potential
- propagation of the action potential
- repolarization
- initial ionic conditions restored
Describe action potential initiation and generation
- a stimulus changes the permeability of the neuron’s membrane to sodium ions
- sodium channels now open, and sodium (Na+) diffuses into the neuron
- the inward rush of sodium ions changes the polarity at that site and is called “depolarization”
- a graded potential (localized depolarization) exists where the inside of the membrane is more positive and the outside is less positive
- if the stimulus is strong enough and sodium influx great enough, local depolarization activates the neuron to conduct an action potential (nerve impulse)
Describe propagation of the action potential
- if enough sodium enters the cell, the action potential (nerve impulse) starts and is propagated over the entire axon
- “all-or-none response” means the nerve impulse either is propagated or is not
- fibers with myelin sheaths conduct nerve impulses more quickly
Describe repolarization
- membrane permeability changes again — becoming impermeable to sodium ions and permeable to potassium ions
- potassium ions rapidly diffuse out of the neuron, repolarizing the membrane
- repolarization involved restoring the inside of the membrane to a negative charge and the outer surface to a positive charge
- initial conditions of the sodium and potassium ions are restored using the sodium-potassium pump
- this pump, using ATP, restores the original configuration
- 3 sodium ions are ejected from the cell
- 2 potassium ions are returned to the cell
- until repolarization is complete, a neuron cannot conduct another nerve impulse
