Chapter 11 - Nervous System Flashcards
What is the nervous system responsible for? What does it enable?
Controlling most body functions
- Enables the organism to receive and respond to stimuli form their external and internal environments
How quickly do these signals travel within the nervous system?
100m/s
What is the nervous system composed of? What do they do?
1) Neurons: Specialized nervous tissue
2) Neuroglia: Cells that support/protect the neurons
- They work together to form major organs of the nervous system (brain, spinal cord, complex organs)
How is the nervous system grouped?
1) Central Nervous System (CNS)
2) Peripheral Nervous System (PNS)
Describe the structure of a neuron:
- What do they do?
- What do they consist of?
Neurons are the functional units of the nervous system and are used to convert the electrochemical signals and conduct them throughout the body
They consist of:
- Dendrites: cytoplasmic extensions that receive info and transmit it toward the body
- Cell body (soma): contains nucleus and controls metabolic activity of the neutron
- Axon: long cellular process that transmits impulses (AP) away from the cell body
- Myelin: prevents leakage of signal from axons and allows for faster conduction of impulses
- Nodes of Ranvier: gaps between segments of myelin - where the AP propagates
- Synaptic terminal: axons end in swellings
What is myelin produced from? How do they differ from the CNS to PNS?
Glial cells
- CNS: Oligodendrocytes
- PNS: Schwann cells
What are neurotransmitters?
They are released from the synaptic terminals into synapse (synaptic cleft) which is the gap between the axon terminals of one cell and the dendrites of the next cell
What is the function of neurons?
Specialized to receive signals from sensory receptors or from other neurons in the body
- Signals create action potentials which travel the length of the axons to invade the nerve terminal and causing the release of the neurotransmitter into the synapse
Describe the resting potential:
- At rest? Due to?
- How many millivolts at RP? Meaning?
- What is the difference between inside/outside cell due to?
- How many Na/K pumped in/out? Results in?
- What is the cell more permeable to?
At rest, a neuron is polarized due to unequal distribution of ions between the inside and outside of the cell
- 70mV - meaning the inside is more negative than the outside
- The difference is caused by selective ion permeability of the neuronal cell membrane and is maintained by the active transport of ions by the Na/K pump
- 3Na out and 2K in which results in negative internal environment
- More permeable to K; allows some to move back out via facilitated diffusion
Describe the action potential:
- What happens if the cell is excited (depolarized)?
- When does an AP begin?
- What happens when AP reaches the terminal?
- What happens after the signal has been propagated through a segment of axon?
- What does this accomplish together?
- What is hyper polarization and refractory period?
- The inside of the cell is less negative and more positive, allowing the cell to reach threshold potential then the voltage-gated channels located in the nerve cell membrane open in response
- An AP begins when the voltage gated Na channels open to respond to depolarization, allowing Na to rush into the cell causing rapid depolarization (continuous process) toward the terminal
- Once the AP reaches the terminal, a final voltage-gated channel specific for Ca opens and allows Ca to rush in triggering the exocytosis of synaptic vesicles containing neurotransmitters
- After the signal has been propagated through a segment of axon, the high voltage causes voltage-gated K channels to open allowing K to rush out of the cell - at this point Na channel close and the Na/K pump begins to pump Na out
- Together these processes return the cell to its negative potential (repolarization)
- Hyperpolarization occurs when the neurons voltage shoots past the resting potential and becomes even more negative inside than normal due to K being free to leave the cell which results in the refractory period, a time after an AP during which a new AP is difficult/impossible to occur (this allows time for neuron to regenerate neurotransmitter and that AP moves in forward direction)
What is the all or none response?
- What is stimulus intensity coded by?
If and only if the threshold membrane potential is reached, an AP will occur (fire maximally or not at all)
- Stimulus intensity is coded by frequency of AP and not their magnitude
Describe impulse propagation:
- How is info transferred? Why?
- How is speed increased?
Although axons propagate AP bidirectionally, info transfer only occurs in one direction (dendrite to synaptic terminal) because of the refractory period
- Speed is increased by an increase in diameter of the axon and increase in the myelinated segments of the axon such that the membrane is permeable to ions only in the nodes of Ranvier - “hops from node to node”
Describe the synapse:
- What is it?
- What does the nerve terminal contain? What occurs here?
- When are neurotransmitters removed?
The synapse is the gap between the axon terminal of one neutron (pre-synaptic) and the dendrites of another neutron (post-synaptic); they can communicate with other cells than neurons i.e. muscle cells (effector cells)
- Nerve terminals contain thousands of membrane-bound vesicles full of chemical messengers (neurotransmitters); when the AP arrives at the nerve terminal (depolarization), the synaptic vesicles fuse with the pre-synaptic membrane and released the neurotransmitter into the synapse which diffuses across and acts on a receptor embedded on the post-synaptic membrane - the release of this neurotransmitter leads to depolarization
They are removed in many ways:
1) Taken back up via nerve terminal (reused/degraded)
2) Degraded by enzymes in the synapse (Act)
3) Diffuse out of synapse
Describe the effect of the drug curare:
Blocks post-synaptic nicotinic acetylcholine receptors (i.e. on muscles) so acetylcholine is unable to interact with them
- Muscle relaxation and/or paralysis
- Blocks the ability to constrict muscles
Describe the effect of the drug botulinum toxin:
Prevents the release of acetylcholine from pre-synaptic membrane
- Paralysis
Describe the effect of the drug anti-cholinesterases:
Used as nerve gas and in the insecticide parathion
- Substance inhibits activity of the acetylcholinesterase enzyme that is responsible for degrading acetylcholine released into the synapse
- Results in acetylcholine unable to be degraded and takes affect on post-synaptic membrane
- No coordination of muscle contractions can occur
Describe the different types of neurons:
- Afferent
- Efferent
- Interneurons
- Plexus
- Ganglia
1) Afferent neurons carry sensory info about the external/internal environment to the brain or spinal cord
2) Efferent neurons carry motor commands from the brain or spinal cord to various body parts
3) Interneurons participate only in local circuits
- Links sensory and motor neurons in the brain and spinal cord
- Cell bodies and nerve terminals are in same location
4) Plexuses are a network of nerve fibers
5) Ganglia are clusters of neuronal cell bodies (PNS)
- Called nerve in the CNS
How is the nervous system organized?
- Nervous system is broken down in the the CNS and PNS
- The CNS is then broken down into the brain and spinal cord
- The PNS is then broken down into somatic and autonomic
- The autonomic part of the PNS is further broken down into sympathetic and parasympathetic
What does the CNS consist of?
The brain and spinal cord
What is the brains purpose? What does it consist of? How is it organized?
It is a mass of neurons that resides in the skull that functions to interpret sensory info, form motor plans, and cognitive function
- Consists of outer portion of cell bodies (gray matter) and and inner portion of myelinated axons (white matter)
- The brain is divided into the forebrain, midbrain, and hind brain
Describe the forebrain:
- What does it consist of?
1) Telencephalon
- Major component is the cerebral cortex which is highly convoluted gray matter on the surface of the brain
- This part processes and integrates sensory input and motor responses
- Important for memory and creative thought
- Olfactory bulb is centre for reception and integration of olfactory input (smell)
2) Diencephalon
- Contains that thalamus and hypothalamus
- Thalamus: Relay and integration center for spinal cord and cerebral cortex
- Hypothalamus: Controls visceral functions (i.e. hunger, thirst, sex drive, water balance, BP, temp regulation) and is important for endocrine system control
Describe the midbrain:
It is a relay enter for visual and auditory impulses
- Play important role in motor control
Describe the hindbrain:
- What does it consist of?
- Together, what do they constitute?
1) Cerebellum
- Modulate motor impulses initiated by cerebral cortex
- Maintenance of balance, hand-eye co-ordination, and timing of rapid movements
2) Pons
- Relay center to allow the cortex to communicate with the cerebellum
3) Medulla
- Vital functions (i.e. breathing, HR, GI activity)
- Together = the brainstem
Describe the spinal cord:
- What is it and what does it do?
- What is it structure?
- What is the dorsal horn?
- What is the ventral horn?
The spinal cord is elongated extension of the brain that acts as the conduit for sensory info to the brain and motor info from the brain; it can integrate simple motor responses by itself (reflexes)
- Cross sections shows outer white matter area containing motor/sensory axons, and an inner gray matter containing nerve cell bodies
- Sensory info enters spinal cord through dorsal horn
- Motor info exits spinal cord through ventral horn
