Chapter 17 Flashcards
What are the two divisions of the nervous system in animals?
Central nervous system (Brain and spinal cord) and peripheral nervous system (nerve tissue outside of the brain and spinal cord).
What are the two types of cells in nervous tissue?
Neurons which transmit nerve impulses, and neuroglia which support and nourish neurons.
What are the neurons of the peripheral nervous system?
Sensory, afferent, and efferent.
Describe sensory neurons.
Connected to receptor cells, may have specialized endings. Detect a change in stimuli and conduct and electrical impulse which then travels to CNS.
Describe afferent neurons.
Take info from sensory neurons and move it to spinal column or CNS.
Describe efferent neurons.
After central nervous system has dealt with message that was sent from sensory neurons.
What is an effector?
Efferent neurons send messages to an effector. It is an organ, muscle, or gland that receives messages from CNS via efferent neurons.
Describe an interneuron.
Lie entirely within the CNS- the spinal column. Receive input from sensory neurons. They create circuits to parts of CNS that make decisions.
What type of neuron plays a role in reflex reactions?
Interneurons.
Describe motor neurons.
Cell body is in a spinal column, fiber may be outside. Given processed CNS message from interneurons. Then, motor neurons then give message to efferent neurons which then go on to an effector.
What are the 3 parts of a neuron.
Cell body: Contains the nucleus and other organelles.
Dendrites: extensions that receive signals from other neurons.
Axon: Conducts nerve impulses away from the cell body toward other neurons or effectors.
What is a myelin sheath?
Some axons are covered by a myelin sheath in the PNS. Myelin, a lipid substance which wraps around axons to act as an electrical insulator.
Describe the nodes of Ranvier.
The myelin sheath isn’t continuous. The nodes of Ranvier are gaps in the myelin sheath that play a role in ions diffusing in/out enhancing electrical conduction.
What are schwann cells?
A type of neuroglia that surround axons and deposit lipids. These create the myelin sheath around axons.
What happens if the axon is severed in the PNS and CNS?
PNS: sheath helps with new fiber construction or regeneration.
CNS: myelin sheath doesn’t help with regeneration of severed axons.
What are the 2 types of nervous tissue the CNS is composed of?
Gray matter, white matter.
Describe gray matter.
Contains cell bodies and short, non-myelinated fibres. In the surface layer of the brain, related to senses, emotions, and decision making, also in central part of spinal cord where it is related to muscle movement.
Describe white matter.
Contains myelinated axons that run in tracts. The high myelin content gives the white color. It is deep in the brain, surrounds gray matter in spinal cord. The white matter conducts the messages pass to the different gray matter areas.
What happens when an axon is not conducting an impulse.
The inside of the axon is negative compared to the outside. There is unequal distribution of ions across membrane, more sodium (NA+) outside than inside, and more potassium (K+) inside than outside.
How is resting potential maintained?
Sodium-potassium pump. It actively transports Na+ out and K+ in. The membrane is somewhat permeable to Na+ and K+, tends to diffuse toward lesser concentration.
What is the polarity of a membrane based on?
Generally, more (+) ions outside the membrane than inside. Large, negatively-charged organic ions inside.
What is action potential?
A rapid change in polarity across axonal membrane as impulse occurs. (All-or-none), requires two types of gated channel proteins.
What are the two types of gated channel proteins?
Sodium gated channels, potassium gated channels.
What happens first in the action potential?
Sodium gates open first. Sodium flows down the concentration gradient into the axon. Membrane potential changes from -65 mV to +35 mV. It is called depolarization because inside changes from negative to positive.
Discuss the threshold in action potential.
Axon will fire if the depolarization reaches -55 mV. If it goes more to +35 mV it won’t make the impulse stronger, will just make it happen more often.
What happens second in action potential?
Potassium gates open second. Potassium flows down its concentration gradient out of the axon. Brings potential back to -65mV. Called repolarization because it returns to original negative polarity as K+ exits axon. Goes back to resting potential.
Describe conduction of an action potential in nonmyelinated axons.
Action potential travels down an axon one small segment at a time, as soon as an action potential has moved on, and the previous section undergoes a refractory period… during this period the sodium gates are unable to reopen.
Describe the refractory period.
For a short period, Na+ channels are inactivated. New stimuli won’t make them open, will go to resting potential. When able to open, Na+ rushes in again and depolarize and can work again.
What is saltatory conduction?
Jumps from node to node.
What is the synapse?
The region where each terminal lies close to either the dendrite or cell body of another neuron.
What is an axon terminal?
Fine ending of axon that is tipped by a small swelling.
Describe a synaptic cleft.
A tiny gap that separates two neurons at a synapse.
What is a presynaptic neuron?
The membrane of the 1st neuron.
What is a postsynaptic neuron?
The membrane of the 2nd neuron.
What does a neurotransmitter do?
Carries out communication between two neurons. The neurotransmitters are stored in synaptic vesicles.
When are neurotransmitters released?
When action potential reaches axon terminal. There is a sudden rise in Ca2+ stimulates synaptic vesicles to merge with the presynaptic membrane.
What signals can a single neuron receive?
Many different types like: excitatory signals that have a depolarizing effect (bring neuron closer to threshold). Inhibitory signals that have a hyperpolarizing effect (away from threshold).
What is synaptic integration?
The summing up of excitatory and inhibitory signals which determines whether an action potential will travel along an axon.
What happens once a neurotransmitter has been released into a synaptic cleft and has initiated a response?
It is removed from the cleft, and in some synapses it is inactivated by enzymes. The short existence of neurotransmitters prevents repeated stimulation.
How do many drugs affect the system?
Interfering with neurotransmitters and may block and inhibit, or make hyperactive.
What makes up the CNS?
The spinal cord and the brain. Sensory information is received, and motor control is initiated.
What does the brain do?
Controls or influences bodily functions like breathing, heart rate, body temperature, and blood pressure.
What are the brain and the spinal cord protected by?
Bone.
What are meninges?
Protective membranes that wrap around the brain and spinal cord.
What is Cerebral spinal fluid?
Fills the spaces between the meninges and cushions and protects the CNS.
What does individual vertebra do?
Protects the spinal cord. Cushioned and separated by intervertebral disks.
Describe the structure of gray matter.
Shaped like an “H”. Dorsal root- sensory fibres entering gray matter of spinal cord. Transmits info from the PNS to the spinal cord. Ventral root- motor fibres leaving gray matter, carries signals away from CNS to organs, muscles, and glands.
Describe structure of white matter.
Surrounds gray matter. Ascending and descending tracts. Ascending tract is located dorsally, and descending tract is located ventrally.
What is a reflex arc?
When action potential never travels to the brain, and is dealt with right at the spinal cord.
What are the four major areas of the brain?
The cerebrum, the diencephalon, the cerebellum, and the brain stem.
Describe the cerebrum.
The largest portion of the human brain. The last centre to receive sensory input and carry out integration before voluntary motor responses.
Describe the cerebral hemispheres.
Divided by longitudinal fissure but connected by the corpus callosum. Covered by a convoluted layer or gray matter.
What is the cerebral cortex?
A thin, highly convoluted outer layer of gray matter that covers the cerebral hemispheres. Each fold is called a gyrus.
What are association areas?
All about integration of information, help to do multiple tasks at once.
What do association areas involve?
Somatosensory, takes info from muscles and skin.
Visual, takes info from seeing help lower level decisions, also help recognize.
What are processing centres?
Receive from association areas. Perform higher level functions. Integration at this area help with critical thinking.
What is central white matter?
A pathway, main function is to transfer information to the association areas.
What is the hypothalamus?
An integrating centre for homeostasis.
What is attached to the hypothalamus?
Pituitary gland.
What is the thalamus?
A sensory relay centre. Receives all sensory input. Integrates the information and send to the cerebrum. Involved in the arousal of the cerebrum.
What is the cerebellum?
Receives sensory input from all the joints, muscles, etc. Deals with body part position. Sends commands to skeletal muscles. Concerned with position and posture.
What does the brainstem contain?
The midbrain, pons, and medulla oblongata.
Describe the midbrain.
Relay centre for tracts passing between cerebrum and cerebellum and/or spinal cord.
Describe the pons.
Called a “bridge”. Function is to relay messages from cerebral cortex and cerebellum. Part of dreams and sleep.
Describe the medulla oblongata.
Regulates vital functions. Contains reflex centres.
What is the PNS divided into?
The somatic system, and the autonomic system.
Describe the somatic system.
Serves the skin, skeletal muscles, and tendons. Includes nerves that carry sensory information from receptors to the CNS. Carries motor commands away from the CNS to skeletal muscles.
What does the autonomic system do?
Regulates the activity of cardiac and smooth muscle and glands.
What are the two divisions of the autonomic system?
Sympathetic nervous system, and parasympathetic system.
What is the sympathetic nervous system important for?
Emergency situations. Fight or flight.
What is the parasympathetic division?
Includes a few cranial nerves and fibres that arise from the spinal cord. Promote rest and digest.
