Nervous System Flashcards
what is the nervous system responsible for?
- controlling body functions, enabling organisms to receive and respond to stimuli from external and internal environments
- signals travel quickly 100m/s resulting in information transmission much faster than the endocrine system
what is the nervous system composed of
- neurons (specialized nervous tissue) and neuroganglia (cells that support neurons)
- work ti form the major oragans of the nervous system (brain, spinal cord and sensory organs)
- divided into central NS and peripheral NS
what are the components of a neuron
- neuons convert stimuli into electrochemical signals and conduct them through the nervous system
- each neuron consists of denrites, a cell body and an axon
- denrites = cytoplasmic extensions that recieve information and transmit it towards the cell body
- cell body (soma) = contains the nucleus that controls the metabolic activity of the neuron
axon = long cellular process that transmits impulses or action potentials away from cell body
*axons end in synpatic terminals (also called boutons or knobs)
what covers the axon in most mammalian cells
insulated by myelin
- prevents leakage of signal from axons and allows for faster impulses to be conducted
- gaps between myelin = nodes of ranvier (where action potential actually propogates) via “hoping” conduction
what produces myelin
- glial cells also called oligodendrocytes in the CNS and by schwann cells in the PNS
where are neurotransmitters released?
released in synaptic terminals into the synpase (synpatic cleft)
- this is the gap between axon terminals of one cell and the dendrites on the next
*axons can be very long ex: travel from spinal cord to tip of foot
What are the 4 major cell types in the CNS and their roles
Astrocytes
- maintain integrity of the BBB
- regulate nutrient and dissolved gad conc
- absorb and recycle neurotransmitters
Oligodendrocytes
- Myelinate CNS axons and provide structural framework for CNS
- *Microglia**
- Remove cellular debris and pathogens
Ependymal cells
- line brain ventricles
- aid in the production, circulation and monitoring of cerebral spinal fluid
What are the major cell types of the PNS
Satellite cells
- surround neuron cell bodies in the ganglia
Schwann cells
- enclose axons in the PNS
- aid in myelination of some peripheral axons
what is the function of neurons
- specialized to recieve signals from sensory receptors and from other neruons
- signals create action potentials whcih trevel length of axon to invade the nerve terminal causing neurotransmitter release @ synapse
what is the resting potential
- potential difference at rest between the extracellular space and the intracellular space
*even at rest neuron is polarized
- typical resting potential is -70mV (inside neuron more neg)
what causes the potential difference
- caused by selective ionic permability of neuronal cell membrane
- maintained by active transport by N+/K+ pump
- 3 Na+ out and 2 K+ in
How does an action potential begin
- if cell becomes sufficiently excited and depolarized (inside more pos) to reach the threshold potential then the voltage agted ion channels in nerve cell mem open
* action potential begins when voltage gated Na+ channels open in response to depolarization
- Na+ rushes down electrochemical gradient INTO cell causing further rapid depolarization
- Na+ influx causes next portion of axon to become depolarized and so on
what happens once the action potential reached the synaptic terminal
- final voltage geted channel *this time calcium* opens alloing Ca2+ to rush in and trigger exocytosis of synpatic vesicles containing neurotransmitters
how does repolarization occur
- occurs after signal has been propogated through a segment of the axon
- the high voltage in that segment causes voltage gated K+ channels to open and K+ rushes down electrochemical gradient
- voltage gated Na+ channels close and the Na+/K+ pump starts to pump Na+ out of the cell
- returns cell to negative potential (repolarization)
what is hyperpolarization
- during repolarization Na+/K+ pump works AND K+, meaning that K+ is still traveling out the cell so the insdie of the cell becomes MORE negative than resting potential
- this called hyperpolarization and results in a refractory period
what is teh refractery period
- period of time after an action potential during which new ones are very difficult - impossible to initiate
- allows neuron time to regenerate neurotransmitter and ensures for action potential to move only in one direction towards the terminal
action potential is called an _____ response
- all or none
- if and only if the threshold membrane potential is reached can an action potential with a consistent size and duration eb rpoduced
- neurons fire maximally or not at all
- stimulus is coded by the frequency of action potentials NOT their magnitude
what is impulse propogation
- although axons can only propogate action potentials bidirectionally information transfer will occur only in one direction: dendrite to synpatic terminal
- thi is bc synpases operate only in one direction bc refractory priods make backward travel not possible
- axons do propgate action potential at different speeds: the greater the diameter of axon the more ehavily its myelinated the faster impulses travel
what is the synapse
- gas between axon terminal of one neuron (presynaptic neuron) and the dendrites of antoher (post synpatic neuron)
what are effector cells
neurons can communicate with post synpatic cells other than neurons such as cells in muscles or glands: called effector cells
how does neurotransmitter release work
- when aciton potential arrives @ enrve terminal and depolarizes it the synpatic cesicles fuse w/ postsynpatic membrane and release neurotransmitter into synpase
- neurotransmitter diffuses across synpase and interacts w/ receptors on post synaptic membrane
- leads to depolarization of post synpatic cell and firing of action potential
how is neurotransmitter removed
- can be taken back up into nerve terminal via uptaker protein where it can be reused or degraded
- can be deraded by enzymes ocated in synpase (acetylcholinesterase inactivates the neurotransmitter acetylcholine)
- can diffuse out synpase
what is the effect of curare
- blocks postsynaptic nicotinic acetylcholine receptors such as those on muscles
- acetylcholine cannot interact leading to muscle relaxation and paralysis by blocking ability to contract muscles
what is the effect of botulinum toxin
- prevents release of acetylcholine from presynaptic membrane and results in paralysis
what is the effect of acetylcholinesterases
- used as nerve gases in the insecticide parathion
- substances inhibit activity of acetylcholinesterase enzyme responsible for degrading acetylcholine released int he synpase
- as a result it acetylcholine is degraded and continues to affect the post synpatic membrane
*no coordinating muscular contraction can take place
what are afferent neurons
- carry sensory information about external and internal environment to braina dn spinal cord
what are efferent neurons
- carry motor commands from brain and spinal cord to various parts of the body (muscles, glands)
what are interneurons
- participate only in local circuits linking sensory and motor neurons in brain and spinal cord
- their cell bodies and nerve terminals are in the same location
what is a network of nerve fibers called
- plexus
*nerves are essentailly bundles of axons covered with connective tissue
Neuronal cell bodies often cluster together, clusters are called ___ in the PNS and ____ in the CNS
ganglia in PNS and nuclei in CNS
what are the branches of the CNS
brain and spinal cord
what are the branches of the PNS
somatic and autonomic
- auonomic is broken into sympathetic and parasympathetic
what is the brain/ what does it consist of
- mass of neurons inside the skull
- functions include interpreting sensory information, forming motor plans and cognitive function (thinking)
- consists of: puter portion of cell bodies called grey matter and innter portion of myelinated axons called white matter
- also divided into forebrain, midbrain and hindbrain
what is another name of the forebrain
prosencephalon
what does the forebrain consist of what are the roles
- telencephalon and diencephalon
Telencephalon
- contains cerebral cortex: highly convoluted gray matter seen on surface of the brain
- processes and integrates sensory input and motor responses: important for creative thought
- olfactory bulb = center for reception and integration of smell related input
Diencephalon
- contains thalamus and hypothalamus
- thalamus = relay and integration center for spinal cord and cerebral cortex
- Hypothalamus = controls visceral functions such as hunger, thirst, sex drive, water balance, blood pressure and temp regulation
- important role in endocrine system
what is te role of the midbrain and waht is the other name
- also called mesencephalon
- relay center for visual and auditory impulses
- important role in motor control
what is the role of the hindbrain
- also called Rhombencephalon
- the hindbrain is the posterior part of the brain
- consists of cerebellum, the pons, and medulla
Cerebellum
- helps to modulate motor impulses initiated by the cerebral cortex and is important in maintenance of balance, hand-eye coordination and timing of rapid movements
Pons
- act as a relay centre to allow the ortex to communicate with the cerebellum
Medulla (medulla oblongata)
- controls many vital functions: breathing, heart rate, gastrointestinal activity
**togethere all 3 of these make the brainstem
what is the spinal cord/ its role
- elongated extension of the brain acting as a conduit for sensory information to the brain and motor information from the brain
- can also integrate simple motor responses (reflexes) by itself
what are the components of the spinal cord
- cross section shows outer white matter containing sensory and motor axons and inner gray matter w/ nerve cell bodies
- sensory information enters via dorsal horn: these cell bodies of sensory neurons are located in the dorsal root ganglia
- all motor information exists the spinal cord via ventral horn
how are different reflexes process by the spinal cord
- in simple reflexes lke knee-jerk sensory fibers (entering through the dorsal root ganglion) synpase directly on ventral horn motor fibers
- other reflexes include interneurons between the senesory and motor fibers alloing for some processing in the spinal cord
Role of peripheral nervous system
- consists of nerve and ganglia
- sensroy nerves enter the CNS and the motor nerves that leave the CNS are part of the PNS
- constains somatic and autonomic each having both motor and sensory components
what is the SNS
- somatic nervous system
- innervates skeletal muscle and is responsible for voluntary movement and reflex arcs (pathways that control motor reflexes
what is the ANS
- autonomic nervous system
- called the involuntary nervous system: operates w/o concious control
- innervates cardian and smooth muscle: smooth msucle is located in areas like blood vessels, digestive tract, bladder and bronchi
- important for blood pressure regualtion, gastrointestinal motility, excretion, respiration, an reproduction
- contains sympathetic and parasympathetic which generally act in opposition to eachother
explain the sympathetic nervous system
- acts to conserve energy and restore body to resting activity levels: rest and digest
- acts to lower heart rate and inc gut motility
- it innervates the thoracic and abdominal viscera called vagus nerve
- acetylcholine is the primary neurotransmitter
describe the parasympathetic nervous system
- responsible for fight or flight responses that ready the body for action in an emergency situation
- increases vlood rpessure and heart rate, inc blood flwo to skeletal muscles, dec gut motility, dilates bronchioles to inc gas exchange
- norepinephrine is the primary neurotransmitter
