Nervous System Flashcards
Organization of the nervous system
In 2 parts:
Central Nervous System - brain and spinal cord
Peripheral Nervous System - spinal and cranial nerves
Divisions of the PNS
Afferent - conducts towards the CNS
Efferent - conducts away from the CNS
Somatic Division of the PNS
Nerves that supply the skeletal muscles. Usually under conscious control
Autonomic Division of the PNS
Nerves that supply smooth muscle, heart muscle, and glands. Not under conscious control. 2 parts: parasympathetic and sympathetic
3 Functions of the Nervous System
- Monitor (Sensory Input)
- Integration
- Response (Motor Input)
Nerve
A bundle of neuronal processes found in the PNS
Nerve Tract
The same as the nerve, a bundle of neuronal processes, but found in the CNS
Ganglion
A collection of cell bodies and synapses which is found in the PNS
Nucleus
A collection of cell bodies and synapses found in the CNS
Center
A synaptic area in the CNS with a specific function (vision center, speech center, etc)
Gray Matter
A general term for unmyelinated nervous tissue.
White Matter
A general term for myelinated nervous tissue
Neurons
The structural and functional units of the nervous system, they conduct actions potentials. They are long lived, amitotic (don’t divide) and have a high metabolic rate.
Structure of a Neuron
Have 3 general regions: input region, conducting region, and output region. Consist of a cell body and one or more slender processes.
Plasma Membrane of the Neuron
This is the site of electrical signaling
Nissl Bodies
Condensations of the rough ER. Composed mainly of RNA and proteins, and function in protein synthesis.
Dendrites
Highly branched cell processes. They are the receptive regions of the neuron. They conduct signals toward the cell body and contain Nissl bodies
Axons
Processes that generate and conduct the AP away from the cell body. Do not contain Nissl bodies, rough ER, or Golgi apparatus. Have a plasma membrane called an axolemma.
Axon Hillock
The region of the cell body which extends into the axon. It is here that the AP is initiated.
Collaterals
Branching of the axons along it’s length.
Telodendria
The terminates of the axon. Each axon can have 10,000 or more. Here is where the neurotransmitter is released.
Myelin Sheath
A white envelope which surrounds the axons of many nerve cells. Made mostly of a white lipid known as myelin. It protects, insulate, and increases the speed of the AP.
Myelination in the PNS
The sheath is formed by Schwann cells which wrap around the axons many times creating many layers of membrane.
Satellite Cell
Regulate the chemical environment of the cell.
Nodes of Ranvier
Small gaps where adjacent Schwann cells meet.
Neurilemma
The nucleus and cytoplasm of Schwann cells wrapped around the myelin sheath forming a tube. When an axon is cut, it forms a regeneration tube which secretes chemicals to help repair the damage which is why most PNS nerve damage is repairable.
Myelination in the CNS
Myelin sheaths are formed by oligodendrocytes. They have nodes of Ranvier, but no neurilemma because each oligodendrocyte myelinates up to 60 different processes. Repair of damaged neurons in the CNS is very limited.
Motor Neurons
Efferent - Conduct impulses away from the CNS.
Sensory Neurons
Afferent - Conduct impulses towards the CNS
Association Neurons
Interneurons - Found within the CNS. Connect the motor and sensory neurons.
Multipolar Neurons
Have more than 2 processes coming off the cell body. Mostly motor and interneurons, most common type found in the CNS.
Bipolar Neurons
Two processes coming off the cell body, one axon and one dendrite. Often associated with special senses like hearing and the retina of the eye.
Unipolar Neurons
There is a single major process coming off the cell body. THis process usually divides into two parts. Most sensory neurons are of this type.
Anaxonic Neurons
Found in the brain
Astrocytes
Most numerous glial cells in the CNS. Have long extensions, hence the star like appearance. They metabolize neurotransmitters, and help control the ionic environment around the neurons.
Oligodendrocytes
Form the myelin sheaths for axons in the CNS
Ependymal Cells
Line the cavities of the CNS and cushion the brain and spinal cord. Have microvilli that circulate the CSF.
Microgliocytes
Small phagocytotic cells, play a role in the destruction of dead tissue and defense against microorganisms
Resting Membrane Potential
Averages about -70mv
Neuronal Responses
First response is the action potential. The second response is the release of the neurotransmitter.
Threshold Point
The weakest stimulus needed to produce an AP.
Subthreshold
Insufficient stimulus. No impulse is produced.
Absolute Refractory
When a membrane patch is generating an AP, that neuron cannot respond to another stimulus
Synapses
The junctions between two or more neurons.
Presynaptic
The neuron which conducts the impulse towards the synapse
Postsynaptic
The neuron which conducts the impulse away from the synapse.
Depolarization
The plasma membrane is becoming less negative. When there is an influx of Na+
Repolarization
The plasma membrane is becoming more negative. K+ is diffusing out, there is a membrane change in permeability.
Second Impulse
A second impulse cannot be generated until the membrane potential is reestablished.
EPSP
Excitatory postsynaptic potential. Causes Na+ and K+ passage. It’s only function is to trigger an AP.
IPSP
Inhibitory postsynaptic potential. Brings the resting potential further away from threshold. It’s function is to inhibit an AP.
Spatial Summation
Several presynaptic neurons fire more or less simultaneously. Stimulation by many terminals at the same time.
Temporal Summation
Several rapid firings cause the neurotransmitter to accumulate.
Divergence
There are relatively few presynaptic neurons and many postsynaptic neurons
Convergence
Many presynaptic neurons approach a synapse and relatively few postsynaptic neurons exit the synapse.
Meninges
Three separate membranes that surround the CNS.
1) Dura mater
2) Arachnoid
3) Pia mater
Arachnoid
Second or middle membrane of the meninges. Its very delicate and web-like and is separated from the inner meninges by a large subarachnoid space which is filled with CSF.
Cerebrospinal Fluid (CSF)
One of the protective layers of the CNS. It consists of a fluid which fills the cavities of the CNS and acts as a shock absorber.
Ventricles
The 4 large cavities of the brain. 1&2 located in the cerebral hemispheres, 3 in the diencephalon, and 4 in the hindbrain.
Telencephalon
The most anterior region of the brain. It’s largest and most obvious structure is the cerebrum.
Cerebrum
Involved with consciousness, no functional area acts alone. Composed of 2 hemispheres separated by a longitudinal fissure. Each hemisphere is concerned by the function of the opposite side of the body, and each has special, unique functions.
Fissure
Deep depression in the brain surfaces.
Sulci
Lesser depressions in the brain surfaces. The elevations between the sulci are known as convolutions or gyri.
Cerebral Cortex
Several millimeters of gray matter covering the outer surface of the cerebrum.
Blood Brain Barrier
Helps ensure brain environment remains stable by relatively impermeable capillaries. Only substances that pass freely are H2O, nutrients, essential amino acids, and electrolytes.
Basal Cerebral Nuclei
Gray matter found deep within the cerebral white matter. Precise function is not really known. Might have something to do with initiating slow movements.
Bulk of the Inner Brain Mass
Made of myelinated tracts and is therefore white matter.
Projection Fibers
Vertical; connect hemispheres with lower brain or spinal cord. Ties the cortex to the rest of the nervous system.
Commissural Fibers
Horizontal; connect gray matter of two hemispheres. Helps the communication between the two hemispheres.
Association Fibers
Horizontal; connect the gyri and loves of the same hemispheres. Transmit impulses.
Lobes of the Hemispheres
4 lobes. Frontal, parietal, temporal, occipital. Insula is sometimes considered a 5th lobe.
Primary Sensory Area
Located in the parietal lobe. It interprets and localizes the origins of touch, pressure, temperature, and pain.
Visual Area
This region interprets visual patterns and is located on the temporal lobe.
Gustatory Area
Taste interpretation occurs here. Located on the parietal lobe.
Olfactory Area
This area is located on the temporal lobe and frontal lobe, it interprets smell
Werickes
Special speech area on the temporal lobe.
Primary Motor Area
Located on the frontal lobe. Controls specific muscles and groups
Premotor Area
Located on the frontal lobe, anterior to the primary motor area. Controls the sequencing of muscle contraction in skilled movements.
Frontal Eye Field Area
Located on the frontal lobe and controls the voluntary scanning movement of the eyes.
Broca’s Area
Translates thoughts into speech. Located on the frontal lobe.
Association Area
Connect motor and sensory areas together. Concerned with the higher functions, memory, judgement, intelligence, and personality.
General Interpretive Area (Gnostic)
Damage to this area results in becoming an imbecile as it is impossible to convert sensory stimuli into a logical thought or action.
Basal Ganglia Nuclei
Islands of gray matter deep in the cerebrum. Include the caudate nucleus and the lentiform nucleus. Damage to this area usually results in some type of tremor (Parkinson’s Disease)
Hemisphere Specialization
While the two hemispheres appear anatomically similar, there is definite specialization.
Diencephalon
Part of the forebrain, consists of 3 regions:
- Epithalamus
- Thalamus
- Hypothalamus
Epithalamus
The upper part of the diencephalon, also known as the pineal gland. It secretes melatonin, a hormone that seems to affect reproductive processes and circadian rhythms.
Hypothalamus
Lower region of the diencephalon, most of the internal functions such as respiration, body temperature, water balance, etc. are regulated by this area.
Functional Brain Systems
Networks of neurons which span large distances in the brain. Ex: the limbic system and reticular formation.
Limbic System
Seems to qualitatively evaluate stimuli into pleasurable or not pleasurable. It plays a major role in emotional responses including rage, fear, hunger, and sexuality.
Brainstem Components
Midbrain, pons, medulla oblongata
Cerebellum Anatomy
Composed of two symmetrical hemispheres and a central portion known as the vermis. Has a thin outer layer of gray matter and an inner mass of white matter.
Cerebellum Function
Functions in two related areas; motor coordination and equilibrium. Helpts promote smooth voluntary movements that are precise and economical.
Cerebellum Damage
Results in movements which are stiff and robot-like and a loss of ability to maintain balance.
Reticular Formation
Mass of gray matter that extends the entire length of the brain stem from the medulla to the diencephalon. Major function is the maintenance of the alert and aroused state.
Anatomy of the Spinal Cord
31 pairs of spinal nerves. Each nerve is connected to the spinal cord by two roots, the dorsal and ventral root. Consists of both gray and white matter, the gray matter is in the shape of an H.
Posterior Horns of the Spinal Cord
Contain mostly interneurons.
Anterior Horns of the Spinal Cord
Contains cell bodies of motor neurons
Gray Commissure of the Spinal Cord
Connects masses of gray matter, enclosed central canal. Cross-bridge between the H.
Olfactory Nerve
Sensory. Receptors found in olfactory epithelium conduct impulses from the olfactory tract to the olfactory center.
Abducens Nerve
Motor. Supplies the extrinsic muscles of the eye.
Vestibulocochlear Nerve
Sensory. Conducts hearing and equilibrium information from the inner ear.
Vagus Nerve
Mixed. Controls most of the muscle movement and receives sensory from the visceral organs. Contains 90% of the entire parasympathetic outflow. Gives rise to 3 parasympathetic plexuses.
Accessory Nerve
Motor. Controls swallowing and the movements of the head. Also controls the junction between the the cranial and spinal roots.
Spinal Nerves by Region
- Cervical (8)
- Thoracic (12)
- Lumbar (5)
- Sacral (5)
- Coccygeal (1)
Reflexes
Most reflexes are spinal reflexes. Info may be transmitted to the brain, but its the spinal cord, not the brain that is responsible for integration of sensory input and of responses transmitted to the motor neurons.
Narcolepsy
Involuntary lapses into sleep
Insomnia
Chronic inability to sleep
Syncope
Fainting
Coma
Unconsciousness with little chance of waking
Sleep
A loss of consciousness that occurs on a daily basis, but you can be roused from it.
Stroke
Loss of blood circulation to an area of the brain and subsequent neuronal death. The most common nervous system disorder
Function of the ANS
Functions to maintain the vegetative activities of the body
The ANS is controlled by
The reticular formation
General Anatomy of the ANS
Both divisions have efferent pathways which consist of two neurons. The first neuron is preganglionic and arises in the CNS, the second neuron is postganglionic, arises from a ganglion outside the CNS and runs to the target organ.
Anatomy of the Sympathetic Division
Preganglionic fibers are short, postganglionic fibers are long. Collateral ganglia along with their postganglionic fibers form sympathetic plexuses (3 of them).
Adrenal Medulla
The inner portion of the adrenal glands. They release epinephrine and norepinephrine into the blood.
Anatomy of the Parasympathetic Division
The preganglionic neuron is much longer than the postganglionic neuron.
3 Parasympathetic Plexuses
- Cardiac
- Pulmonary
- Esophageal
Acetylcholine
Transmitter for the preganglionic fibers of both divisions of the PNS, and the postganglionic fibers of the parasympathetic division.
Norepinephrine
Transmitter for the postganglionic fibers of the sympathetic division
Neurotransmitter Exceptions
The postganglionic fibers which innervate the sweat glands are derived from the sympathetic division but release acetylcholine instead of norepinephrine.
Parasympathetic Division
Associated with the vegetative activities of the body
Sympathetic Division
Associated with the “fight or flight” response of the body.
Special Effects of the Sympathetic Division
Accelerates the heart, inhibits the digestive system, dilates the pupil, decreases secretion in the digestive system, and makes the sweat glands secrete.
Special Effects of the Parasympathetic Division
Slows the heart, stimulates the digestive system, constricts the pupil, and increases secretion in the digestive system.
Role of the Hypothalamus
Coordinates ll the activities of the ANS, it’s the central integrating center for virtually all autonomic function, including the regulation of body temperature.
