Chapter 11 Highlights Flashcards
Anatomical divisions of the nervous system
- Central nervous system
- Peripheral nervous system
Central nervous system
Brain and spinal cord
Brain
- Billions of nerve cells
- Protected by bones of skull
Spinal cord
- Begins at foramen magnum
- Continues through vertebral foramina of cervical to first or second lumbar vertebra
- Millions of neurons, fewer than brain
- Enables brain to communicate with most of body below head and neck
Peripheral nervous system
All nerves in the body outside the protection of the skull and vertebral column
Nerves
- Axons of neurons bundled together with blood vessels and connective tissue
- Carry signals to and from CNS
- Classified by origin or destination
Cranial nerves
12 pairs of nerves traveling to or from brain
Spinal nerves
1 pair of nerves traveling to or from the spinal cord
Functional divisions of the nervous system
- Sensory
- Motor
Sensory (afferent) nervous system
- Gathers info about internal and external environments
- Carries signals from receptors to the spinal cord and the brain
Divisions of afferent division
- Somatic sensory division
- Visceral sensory division
Somatic sensory division
- Special sensory division
- Carries signals from skeletal muscles, bones, joints, and skin, organs of vision, hearing, taste, smell, and balance
Visceral sensory division
Transmits signals from heart, lungs, stomach, kidneys, and urinary bladder
Divisions of efferent division
- Somatic motor division
- Autonomic nervous system
Somatic motor division
- Neurons transmit signals to skeletal muscle
- Voluntary control
Autonomic nervous system
- Neurons carry signals to thoracic and abdominal viscera
- Critical for maintaining homeostasis
- Regulates secretion of certain glands, contraction of smooth muscle and cardiac muscle
- Involuntary
Neurons
Excitable cells responsible for sending and receiving signals as action potentials
Parts of a neuron
- Cell body (soma)
- Dendrites
- Axon
Soma
- Most metabolically active region
- Manufactures proteins
Dendrites
- Short, branched processes
- Receive input from other neurons
Axon
Generate and conducts action potentials
Axon hillock
Where axon originates from cell body
Axon terminals
- Synaptic bulbs
- Components that communicate with target cell
Interneurons
Relay info within CNS b/t sensory and motor neurons
Neuroglial cells
- Astrocyte
- Oligodendrocyte
- Microglial cell
- Ependymal cell
- Schwann cells
- Satellite cells
Function of Astrocyte
- Anchor neurons and blood vessels
- Regulate the extracellular environment
- Facilitates the formation of the blood brain barrier
- Repair damaged tissue
Function of Oligodendrocyte
Myelinate certain axons in the CNS
Function of Microglial cell
Act as phagocytes
Function of Ependymal cell
- Line cavities
- Manufacture and circulate cerebrospinal fluid
- Ciliated cells
Function of Schwann cells
Myelinate certain axons in the PNS
Function of Satellite cells
Surround and support cell bodies
White matter
- Composed of myelinated axons
- Appear white
Gray matter
- Composed of neuron cell bodies and unmyelinated axons
- Appear gray
Voltage-gated channels
Open in response to changes in voltage across membrane
Graded potentials
- Small local changes in potential of neuron’s plasma membrane
- Triggers for long-distance action potentials
Effects of graded potentials
- Depolarization
- Hyperpolarization
Depolarization
- Positive charges enter cytosol
- Make membrane potential less negative (change from -70 to -60 mV)
Hyperpolarization
- Either positive charges exit or negative charges enteer cytosol
- Makes membrane potential more negative (change from -70 to -80 mV)
Action potential
Uniform, rapid depolarization and repolarization of membrane potential
States of voltage-gated potassium channels
- Resting
- Activated
Resting state
- Channels are closed
- No potassium ions are able to cross plasma membrane
Activated state
- Channels are open
- Potassium ions are able to flow down concentration gradients
Action potential steps
1) Graded potential depolarizes (usually -55 mV)
2) Voltage-gated sodium channels activate and sodium ions flow into axon causing depolarization (positive feedback loop amplified output)
3) Sodium ion channels inactivate and voltage-gated potassium ion channels activate; Na ions stop flowing into axon; K begins exiting axon as repolarization begins
4) Na channels return to resting state and repolarization continues
5) Axolemma may hyperpolarize before K ion channels return to resting state, then return to resting potantial
Refractory Period
- Period after neuron has generated action potential
- Neuron cannot be stimulated to generate another action potential
Phases of refractory period
- Absolute
- Relative
Absolute refractory period
No additional stimulus is able to produce additional action potential
What channels are open/closed during absolute refractory period?
- Coincides with voltage-gated Na channels being activated and inactivated
- Na channels may not be activated until they return to resting states
Relative refractory period
- Follows immediately after absolute refractory period
- Only strong stimulus can produce action potential
What channels are open/closed during relative refractory period?
- Na channels are at resting state, able to open again
- K channels are activated and membrane is repolarizing or hyperpolarizing
- Takes MUCH larger stimulus to trigger action potential
Conduction speed
- Rate of propagation
- Influenced by both axon diameter and myelination
- Determines how rapidly signaling can occur within nervous system
What makes conduction speed greater?
- Larger diameter –> faster
- Lower resistance
Saltatory conduction
- In myelinated axons
- AP jumps from node to node (nodes of Ranvier)
Continuous conduction
- In unmyelinated axons
- Every section of axon has to conduct action potential
Axon classification by conduction speed
- Type A
- Type B
- Type C
Type A
- Fastest conduction speeds
- Largest diameter
- Myelinated
- Sensory and motor axons associated with skeletal muscle and joints
Type B
- Slower conduction speeds
- Mostly myelinated with intermediate diameter axons
- Efferent fibers of autonomic nervous system and some sensory axons
Type C
- Slowest conduction speeds
- Smallest diameter fibers
- Unmyelinated axons include efferent fibers of ANS and sensory axons
- Transmits pain, temperature, and certain pressure sensations
What happens at the chemical synapse?
- More complicated than neuromuscular junctions
- Multiple neurons secreting many different types of excitatory or inhibitory neurotransmitters
Steps occurring at the chemical synapse
1) Action potential in presynaptic neuron triggers opening of voltage-gated Ca ion channels in axon terminal
2) Ca ions cause synaptic vesicles to release neurotransmitter into synaptic cleft
3) Neurotransmitters bind to receptors on postsynaptic neuron
4) Ion channels open, leading to local potential and possibly action potential if threshold is reached
Postsynaptic potentials
Local potentials in membranes of postsynaptic neuron
Excitatory postsynaptic potential (EPSP)
- Membrane potential of postsynaptic neuron moves closer to threshold
- Caused by small local depolarization
Inhibitory postsynaptic potential (IPSP)
- Membrane potential of postsynaptic neuron moves farther away from threshold
- Caused by small local hyperpolarization
Types of summation
- Temporal
- Spatial
Temporal summation
- Neurotransmitter released repeatedly from single presynaptic neuron
- Short-lived, so must be generated quickly to reach threshold
Spatial summation
Simultaneous release of neurotransmitters from axon terminals of many presynaptic neurons
