Unit 4 Flashcards
homeostasis
an equilibrium (steady state) between an organism’s various physiological functions, and between the organism and the environment
a balance in repsonse to continually changing conditions in both the internal and external environments
components of control systems
monitor - special sensors located in the organs of the body detect changes in homeostasis
coordinating centre - receives message from sensors and relays information to appropriate regulator
regulator/effectors - restores normal balance
the activity of various specialized parts of an animal are coordinated by the two major systems of internal communication:
nervous system - involved with high-speed messages
endocrine system - involved in production, release, and movement of chemical messengers
types of chemical signals
hormones - produced by endocrine system to convey info between organs of the body
pheromones - chemical signals used to communicate between different individuals
neurotransmitters - chemical signals between cells on a localized scale
negative feedback system
most homeostatic control systems are negative feedback systems
prevent small changes from becoming too large
a relationship in which the response is opposite to the stimulus
the body is self correcting by the use of negative feedback
turns off when returns to normal
positive feedback system
process by which a small effect is amplified
a relationship in which the response is the same as the stimulus
leads to instability and possibly death
must be turned off by outside event
role of nervous system
the human brain is the control centre of the body
the nervous system monitors and controls body processes, from automatic functions (such as breathing) to activities that involve fine motor coordination, learning and thought (ex. playing piano)
two major divisions of the nervous system
central nervous system - consists of brain and spinal cord; integrates and processes information sent by nerves
peripheral nervous system - network of nerves that carry sensory messages to CNS and send information from the CNS to muscles and glands; subdivided into afferent and efferent system
subdivisions of peripheral nervous system
afferent system (carrying toward) - receives input through receptors and transmits input to CNS by afferent neurons; the afferent/sensory neuron carries impulses from sensory receptors to CNS efferent system (carrying away) - efferent neuron carries impulses from CNS to effectors (muscles and glands); further subdivided into somatic and autonomic system
subdivisions of efferent system
somatic system - composed of efferent (motor) neurons that carry signals to skeletal muscles in response to external stimuli; essentially voluntary
autonomic system - communicates with smooth muscles and glands; controls mainly involuntary processes such as digestion, secretion by sweat glands, blood circulation and contraction of smooth muscles; further subdivided into sympathetic and parasympathetic systems
subdivisions of the autonomic system
sympathetic division - increases energy consumption and prepares body for action; dominates in situations that involve stress, danger, excitement or strenous physical activity; signals from sympathetic division increase force and rate of heartbeat, raise blood pressure by vasoconstriction, dilate air passages in lungs, induce sweating, and dilate pupils
parasympathetic division - stimulates body activities that acquire and conserve energy; dominates during quiet, low-stress situations, such as relaxation; effects of sympathetic division are reduced (rapid heartbeat, elevated blood pressure) and maintenance activities such as digestion predominate
neurons
nerve cell
structural and functional unit of nervous system
consist of a nucleus, cell body, dendrites, and axons
specialized to respond to physical and chemical stimuli, conduct electrochemical signals, and release chemicals that regulate body processes
neurons are organized into tissues called nerves
dendrites (neurons)
highly branched projections which form treelike outgrowth at one end of neuron
receive nerve impulses or signals and transmit them towards cell body
cell body (neurons)
contains nucleus and most of the organelles
site of cell’s metabolic reactions
processes input from dendrites - if input large enough, relayed to axon and impulse is initiated
axon (neurons)
specialized projection that conducts impuses away from cell body to another neuron or an effector
terminal end branches into many fibres
branching end as small button-like swellings called axon terminals
axon terminal (neurons)
releases chemical signals into space between neuron and the receptors or dendrites of neighbouring cells
glial cells
support cell of nervous system
do not conduct electrical signals
nourish neurons, remove their wastes, and defend against infection
provides a supporting framework for all nervous system tissue
schwann cells
type of glial cell that forms myelin by wrapping themselves around axons
myelin sheaths are the fatty, insulating layer around the axon which protects neurons and speeds up the rate of nerve impulse transmission
nodes of ranvier
regularly occurring gap between sections of myelin sheaths along axon
expose axon membrane directly to extracellular fluids
speeds up the rate at which electrical impulses move along axons
neural signalling
reception - detection of stimulus, performed by neurons and by specialized sensory receptors (in eyes and skin)
transmission - movement of message along neuron to either another neuron of muscle or gland
integration - sorting and interpretation of multiple neural messages and determination of appropriate response
response - output or action
three functional classes of neurons involved in neural signalling
afferent neurons (sensory neurons) - transmit stimuli collected by their sensory receptors to interneurons in CNS interneurons - integrate neural message and relay impulses between afferent and efferent neurons, found primarily in brain and spinal cord (CNS) efferent neurons - carry response signal away from interneurons to effectors, which are muscles or glands; efferent neurons that carry signals to skeletal muscles are called motor neurons
reflex and reflex arc
reflex - sudden, involuntary response to certain stimuli (ex. jerking hand away from hot or sharp object)
reflex arc - simple connections of neurons that result in response to a stimulus; neural circuit that travels through spinal cord but does not require coordination of brain
how does the neural arc work
ex. receptors in skin sense pressure of cactus
initiate an impulse in afferent (sensory) neuron
impulse activates interneuron in spinal cord
interneuron signals motor neuron to instruct muscle to contract and withdraw hand
three factors maintain resting membrane potential
- large negatively charged proteins in intracellular fluid too large to pass through cell membrane
- plasma membrane has ion-specific channels that allow passive movement of ions across membrane. K+ channels tend to be open at resting potential, move along concentration gradient. Na+ cannot move into cell as easily. interior of cell more negative than exterior.
- NA+/K+ active transport pump pumps 3 Na+ out of cell for every 2 K+ pumped in. Net positive charge outside of cell.
how does a nerve impulse travel?
nerve is stimulated, an action potential is triggered and the neuron reaches threshold potential. Na+ channels in cell membrane open, Na+ ions rush into the axon. Charges reverse at this point on the neuron. cell becomes depolarized to +40 mV. change in charge opens next Na+ gates down the line. Na+ ions continue to diffuse into the cell like a domino effect through these gates.
As a result of the change in membrane potential, Na+ channels close and K+ channels open. K+ ions rush out of the axon. Membrane becomes hyperpolarized to -90mV before the K+ channels close.
Resting potential is restored and the membrane is repolarized to -70mV by the sodium-potassium pump.
action potential propagates down axon to next neuron
how does the nerve reset itself?
Na+ needs to move back out and K+ needs to move back in, both against a concentration gradient
this is accomplished with active transport in a sodium-potassium pump which requires ATP
3 Na+ out, 2 K+ in
resets charge across the membrane
refractory period
a result of a temporary inactivation of the Na+ channels
during the refractory period after an action potential, a second action potential cannot be initiated
myelinated nerve impulse
in myelinated neurons, action potentials are generated only at the nodes of Ranvier which contain many voltage-gated sodium channels. it is the only area of myelinated axons that have enough sodium channels to depolarize the membrane to cause action potential.
saltatory conduction
conduction of an impulse along a myelinated neuron
unmyelinated nerve impulse
conduction of nerve impulse is continuous and much slower than saltatory conduction along myelinated axon
synaptic terminal & synapse
synaptic terminal - passes information across the synapse in the form of chemical messengers called neurotransmitters
synapse - a junction between an axon and another cell
presynaptic cell vs postsynaptic cell
presynaptic cell - a neuron where info is transmitted from
postsynaptic cell - the next neuron, a muscle, or a gland cell
membrane potential & resting membrane potential
membrane potential - electrical charge separation across a cell membrane; a form of potential energy
resting membrane potential - potential difference across the membrane in a resting neuron (-70 mV)
action potential
the movement of an electrical impulse along the plasma membrane of an axon.
the change in charge that occurs when the gates of the K+ channels close and the gates of the Na+ channels open after a wave of depolarization is triggered
signal transfer across a synapse
neurotransmitters carry neural signal. when an action potential arrives at the end of a presynaptic neuron, the impulse causes intracellular sacs that contain neurotransmitters to fuse with the membrane of the axon. these sacs, called synaptic vesicles, release their contents into the synaptic cleft (small gap between neurons) by exocytosis
when the neurotransmitters reach the postsynaptic membrane, they bind to specific receptor proteins which trigger ion-specific channels to open.
types of neurotransmitters
excitatory - speed up impulses by causing depolarization of postsynaptic membrane
inhibitory - slow impulses by causing hyperpolarization of postsynaptic membrane
acetylcholine
common neurotransmitter in vertebrates and invertebrates
involved in muscle stimulation, memory formation, and learning
acetylcholine-releasing neurons in brain degenerate in people who develop Alzheimer’s disease
acetylcholinesterase
enzyme which breaks down acetylcholine neurotransmitter
acetylcholinesterase inhibitors such as snake venom and insecticides are neurotoxins
common neurotransmitters
epinephrine (adrenaline) & norepinephrine - fight or flight response
dopamine - widespread in brain; affects sleep, mood, attention & learning; lack of dopamine in brain associated with Parkinson’s disease; excessive dopamine linked to schizophrenia
serotonin - widespread in brain; affects sleep, mood, attention & learning; inadequate amounts of serotonin linked to depression
endorphins - affect our perception of pain / natural pain killers; create a sense of euphoria; opiates bind to the same receptors as endorphins and can be used as painkillers
gray matter vs white matter
consists of neuron cell bodies, dendrites, unmyelinated axons
consists of bundles of myelinated axons
cerebrospinal fluid
filtered from blood and functions to cushion the brain and spinal cord
fills the central canal of the spinal cord and the ventricles of the brain
blood-brain barrier
supplies brain with nutrients (glucose and oxygen)
protects brain by blocking potentially harmful substances such as toxins and infectious agents
caffeine, nicotine, alcohol and anesthetics cross barrier - have rapid effects on brain function
spinal cord
column of nerve tissue that extends out of the skull from the brain, and downward through a canal within the backbone
through the spinal cord afferent nerves carry messages from body to brain for interpretation and efferent nerves relay messages from the brain to effectors
primary reflex centre - contains interneuron circuits that control motor reflexes
what protects the spinal cord
cerebrospinal fluid
the spinal column (vertebrae)
meninges - 3 layers of tough, elastic tissue within skull and apinal column that directly enclose brain and spinal cord
