Chapter 14 Flashcards
(48 cards)
The nervous system and endocrine system work together how?
- they work together to perform the vital function of communication for the body
- communication provides the means to control and integrate the many difference functions performed by organs, tissues, and cells.
The nervous system is made up of what
- the brain
- the spinal cord
- the nerves (most intriguing body system)
The nervous system is organized to detect what
(Stimuli) in the internal and external environment, evaluate that information and respond by initiating changes in muscles or glands
Central nervous system
Brain
Spinal cord
Peripheral nervous system
Cranial nerves
Spinal nerves
Afferent and efferent division
- both the CNA and PNS nerves that form incoming information pathways and outgoing information pathways
Afferent: consists of all of the incoming sensory information - “Carry towards the CNS” Information -> CNS
Efferent: consists of all oof the outgoing sensory information - “carry away from the CNS” CNS -> body
Peripheral nervous system
- somatic nervous system
- carry information to the somatic effectors
- “Skeletal muscles”
- carry information to the somatic effectors
- autonomic nervous system
- carry information to the autonomic or visceral effectors
“Smooth muscle
Autonomic nervous system
- carry information to the autonomic or visceral effectors
- smooth muscles, cardiac muscles, glands, adipose tissue and other voluntary tissues
- sympathetic division
- “fight or flight” - parasympathetic division
- “resting and digesting”
The two main types of cells that compose the nervous system
Neurons: excitable cells that conduct the impulses that make possible all nervous system
- “wiring of the nervous system”
Glia: do not usually conduct information but support the function of neurons
- supporting cells
Types of neuroglia
Astrocytes: provide metabolic (feeding) and structural (BBB) to neurons
Microglia: phagocytic cells that help remove bacteria and debris
Ependymal cells: form thin sheets that line fluid-filled cavities in the brain and spinal cord
Oligodendrocytes: produce the fatty myelin sheath around nerve fibers in the CNS
Schwann cells: produce myelin sheath around nerve fibers in the PNS
The three parts of a neuron
Cell body (soma): main part of the cell, has the nucleus and most of the cytoplasm and organelles
Dendrites: small, slender extensions of the cell body, which receive incoming information
Axon: long, slender extension, specialized to conduct electrical impulses away from the cell body
Physiology of a neuron
- neurons generate and transmit action potentials
- an action potential is basically an electrical impulse
- action potentials are the primary means of communication throughout the nervous system
Membrane potential - all living cells, maintain a a difference in the concentration of ions across their membranes
- a difference in electrical charge across a cell’s plasma membrane
- outside the PM has a slight excess of cations
- inside the PM has a slight excess of anions
Functions of Na+/K+ pump
- maintains cell volume
- establishes and maintains resting potential by ongoing active transport of three Na+ out of the cell and two K+ into the cell
Resting potential
Resting potential: measurable difference in voltage across the cell membrane in a resting cell
-> -70 mV
-> interior of cell is negative relative to the exterior
Graded potential
- transient local changes in the resting potential
- may depolarize or hyperpolarize the membrane
Summation
- graded potentials ca add up in space or time
- this additive effect may reach a “trigger point” or threshold, which initiates an action potential
An action potential is a sudden reversal of membrane voltage
Depolarization
Repolarization
Reestablishment of the resting potential
- initiated when graded potentials reach a certain threshold (triggering point)
Depolarization: voltage-sensitive Na+ channels open, Na+ moves into the axon (this reverses the voltage across the membrane, interior becomes +)
Repolarization: Na+ channels close, K+ channels open, K+ moves out of the axon (this restores the initial polarity, becomes temporarily hyperpolarized)
Reestablishment of the resting potential: K+ channels close, the normal activity of the sodium-potassium pump restores resting potential
Steps of the mechanism of action potential
1) when adequate stimulus is applied to the neuron, stimulus - gates Na+ channels open
- causing rapid Na+ diffuse into the cell
2) Threshold potential: the minimum magnitude a voltage fluctuation in the condition zone must have to trigger the opening of a voltage-gated ions channels
- -55mV = threshold
- More, rapid Na+ diffuse into the cell
3) as more Na+ rushes into the cell, the membrane moves rapidly toward 0mV
- continuing, is a positive directly until it reaches + 30mV
4) Na+ gates close automatically (Na+ channels open for the same amount of time and magnitude each action potential
- All-or-none response
5) K+ voltage gated ions channels open (these gates are stimulate at the same time as the Na+ but are slow
- K+ rapidly diffuses out of the cell, returning the cell to RMP
6) Hyperpolarization occurs while the K+ gates close
- at which point the sodium-potassium pump returns the cell to its RMP
All-or-none action potential
- individual neuron threshold sets extent of stimulus needed
- if threshold is achieved, it triggers an action potential
- once triggered, an cation potential is always the same in speed and voltage
Self-propagating
- continues to propagate itself in the next region of the axion
- moves like a wave down the axon, with constant speed and amplitude
The number of action potential/unit time encodes the strength of the stimulus
- stronger stimuli generate more action potentials/unit time
Speed of action potential - always the same for a particular neuron
- can be different in different neurons
- in larger diameter axons, action potentials travel at greater speed
Saltitory glands
- the propagation of action potentials along myelinated axons from one node of Ranvier to the next
- increasing the velocity of action potentials
- “jumping from node to node”
Synapse
- the place where signals are transmitted from one neuron to another
