Chapter 11.1 Thestructures and process of he nervous system Flashcards
Homeostasis
The state of relative stability within the body
- critical for survival because the body can only survive within a narrow range of conditions
The _____ system regulates body structures and processes to maintain ______ despite fluctuations in the _______ and ____ environment.
- nervous
- homeostasis
- internal
- external
The nervous system consist of
brain
spinal cord
nerves that emerge
The nervous system has 2 major divisions
- The CNS
- The PNS
Together the CNS and PNS
control sensory input, integration and motor output
Somatic system
- part of PNS
- associated with the voluntary control of body movements through the skeletal muscles and mediation of involuntary reflex arcs.
- Consist of sensory receptors in the head and extremities, nerves that carry instructions from the CNS to the skeletal muscles
- it is involved in the relay of sensory and motor information to and from the CNS; therefore, it consists of motor neurons and sensory neurons.
What does the CNS consist and what does it do?
- brain and spinal cord
- Integrates and processes information sent by nerves
what does the PNS contain
and what does it do?
- includes nerves that carry sensory messages to the CNS and nerves that send info from the CNS to the muscles and glands
- Includes somatic and autonomic
Autonomic
Control glandular secretions and the functioning of smooth and cardiac muscles
- not voluntary
- contains sympathetic and parasympathetic
Sympathetic nervous system with ex:
prepares body for stress related activities
- dilates pupil
- increase heart rate
- inhibits digestion
- dilates bronchi
Parasympathetic nervous system with ex:
- returns body to routine, day to day operations
- contricts pupil
- slower heart rate
- stimulates digestion
- constricts bronchi
The nervous system is composed of 2 main types of cells:
Neurons and glial cells (cells that support the neurons)
Neurons and the three things they do:
- the basic structural and functional units of the nervous system
- respond to physical and chemical stimuli
- conduct electrochemical signals
- release chemicals that regulate various body processes
Glial cells
- outnumber neurons by about 10-1
- They account for about half of the volume of the nervous system
- nourish neurons, remous their wastes and defend against infection
- provides a supporting framework for al the nervous-system tissue
nerves
Individual neurons organized into tissues
- made up of nerve bundle(s) surrounded by protective connective tissue
- extend neurones throughout the PNS
Sensory input
Sensory neurons gather info from the sensory receptors (senses) and transmit these impulses to the CNS
Integration
Interneurons are found entirely within the CNS. They act as a Link between the sensory and motor neurons. They process and integrate incoming sensory info and relay outgoing motor info.
Motor output
Motor neurons transmit information from the CNS to the muscles, glands and other organs
Reflexes with ex:
Sudden unlearned, involuntary responses to certain stimuli
- Jerking your hand away from a hot object
- Blinking from a sudden object
- Vomiting from irritable food
Reflex arcs (2)
Simple connections of neurons that explain reflexive behaviours
- use very few neurons to transmit messages (very rapid)
Why do you feel pain after you have done a withdrawal action?
A reflex arc moves directly to and from the brain or spinal cord, before the brain centres involved with voluntary control have time to process the sensory information.
Neurons may have different types and shapes but generally, they share four common features:
- Dendrites
- Cell body
- An axon
- Branching ends
Dendrites (2)
- Short branching terminals that receive nerve impulses from other neurons or sensory receptors and relay the impulse to the cell body.
- numerous and highly branched which increases the surface area available to receive information
Cell body (3)
- Contains the nucleus
- the site of the cell’s metabolic reactions
- process input from the dendrites, if the input is large enough, the cell body relays it to the axon, where an impulse is initiated
Axon
- conducts impulses away from the cell body
Axon terminal
- releases chemical signals into the space between it and the receptors or dendrites of neighbouring cells to communicate with adjacent neurons, glands or muscles.
myelin sheath (3)
- Fatty insulating layers
- protects myelinated neurons
- speeds the rate of nerve impulse transmission
Schwann cells (5)
- grey/white
- pns
- type of glial cell
- form myelin by wrapping themselves around the axon
- myelinated= white matter
- unmyelinated= grey matter
- most neurons in PNS are myelinated
How is nerve conduction different from electrical
- more complex and slower
- Nerve conduction depends on the movement of ions across the cell membrane of the axon, not the movement of electrons along an electrical wire
In a resting neuron, the cytoplasmic side of the membrane is:
negative relative to the extracellular side
resting membrane potential
the potential difference across the membrane in a resting neuron is a form of potential energy
- 70mv
- negative on the inside relative to the outside
- provides energy for the generation of a nerve impulse in response to an appropriate stimulus
Polarization and how do neurons become polarized?
The process of generating a resting potential of -70mv
- large protein molecules that are negatively charged present in the intracellular fluid but not the outside of the cell do not pass out of the cell as they are too big
- membrane is impermeable to smaller negatively charged ions such as CL
- Sodium potassium pump
Sodium potassium exchange pump
- uses ATP to transport sodium ions out of the cell and potassium ions into the cell
- three sodium for two potassium
- excess passive accumulates outside of the cell
- Na and K+ still diffuses across the cell following concentration gradient but potassium ions are able to diffuse out of the cell more easily then sodium can move in so positive outside
a nerve impulse consists of a series of
action potentials
In myelinated neurons, action potential occur only at:
Nodes of ranvier because the myelin sheath insulates the axonal membrane that it encircles
depolarized
A neuronal membrane is said to be depolarized if the transmembrane potential is reduced to less than the resting potential of -70mv.
Depolarization is caused when positively charged sodium ions rush into a neuron with the opening of voltage-gated sodium channels.
action potential
if the membrane at the node of ranvier becomes depolarized to -55mv, a dramatic change occurs in the membrane. This is action potential
- all or none event. any depolarization to -55mv to any other amount up to 0 will produce identical action potentials
- brief reversal of electric polarity
Threshold potential
-55mv
repolarized
returned to its previous polarization
Repolarization is caused by the closing of sodium ion channels and the opening of potassium ion channels. Carry positive charge out of the neuron.
refractory period
the brief time where the membrane cannot be stimulated to undergo another action potential
Saltatory conduction
describes the way an electrical impulse skips from node to node down the full length of an axon, speeding the arrival of the impulse at the nerve terminal in comparison with the slower continuous progression of depolarization spreading down an unmyelinated axon.
- the conduction of an impulse along a myelinated neuron
multiple sclerosis
The breakdown of the myelin sheath surrounding the axons in the CNS
Synapse
The connection between two neurons or a neuron and an effector
Neuromuscular junction
synapse between a motor neuron and a muscle cell
Synpatic cleft
most neurons are not directly connected but have a gap between them
Neurons are not close enough for the impulse to jump from one to the other.
Neurotransmitter
chemical messengers
carry the neural signal from one neuron to another.
can also carry neural signal from a neuron to an effector such as a gland or muscle fibre
Explain how signal transmit across a synapse
When action potential arrives at the end of the neuron, the impulse causes sacs that contain neurotransmitters to fuse with the membrane of the axon.
These sacs called synaptic vesicles release their contents into the synaptic cleft by exocytosis.
The neurotransmitter diffuse across the synapse to reach the dendrites of the postsynaptic neuron or cell membrane of an effector.
neurotransmitter bind to specific receptor proteins in the membrane and trigger ion specific channels to open.
if neurotransmitter is excitatory:
receptor proteins will trigger ion channels that open to allow positive ions such as sodium to flow into the postsynaptic Neuton. As a result, the membrane becomes depolarized.
the membrane of the neuron cannot experience an action potential but it lowers threshold level. The combined effect of all the stimuli spreads across the cell body. if the excitatory stimuli is strong enough, the depolarization will reach the point at which the axon is connected to the cell body and impulse will be generated
If the neurotransmitter is inhibitory:
The receptor will trigger potassium ions to flow out resulting in more negative transmembrane potential and hyper polarization.
After the neurotransmitter has had its effect:
Enzymes break it down and inactivate it so that its components can be reabsorbed by the presynaptic cell
Acetylcholine
A neurotransmitter that crosses a neuromuscular junction.
Excites the muscle cell membrane, causing depolarization and contraction of the muscle fibre
cholinesterase
an enzyme that breaks down acetylcholine so it can be removed from the protein receptors allowing the ion channels to close and membrane to repolarize.
