Nervous System Flashcards
Draw the nervous system organization chart
refer to slides
What are the two cell types that nervous tissue is composed of?
Neurons
Glial cells
What are the three parts of a neuron and what is their function?
Axons - info moves away from cell body
Dendrites - info moves towards cell body
Cell bodies - integrates in and outgoing information
What are the three classification of neurons based on structure? Where are they located?
Multipolar - CNS
Pseudounipolar - PNS
Bipolar - sensory organs
What are the four classification of neurons based on function? Where are they located?
- Sensory (afferent): PNS->CNS
- Motor (efferent): CNS->muscles/glands
- interneurons: relay info between neurons within the CNS
- specialized receptors transducers: convert stimuli to signal
What are 4 types of glial cells?
Oligodendrocytes
Astrocytes
Ependymal cells
Microglia
Which are more abundant, glial or neuronal cells?
glial, 10x more abundant
What are the 5 functions of glial cells?
- provide structural support to nervous tissue
- participate in myelin formation (oligodendrocytes)
- secrete glutamate: can modulate excitatory level of neurons (astrocytes)
- some have phagocytic activity (microglia)
- contant both blood vessels and neurons (transport of nutrients including glucose/O2)
What do neurons not store?
glucose and O2
What does white vs grey matter correspond to?
Grey - cell bodies
white - bundles of neuron processes with the white appearance due to myelin sheaths
What are nerves?
bundles of axons, run from or to CNS
Where are cell bodies of sensory neurons located?
in clusters named ganglia outside of CNS
Where are cell bodies of motor nerves located?
in well-defined area of the CNS (brain/spinal cord)
What is myelin?
white lipid that surrounds nerve fibers, glial cells wrapped around axon
What type of insulator is the myelin sheath?
electrical
How is AP transmitted in myelinated axons?
Nodes of ranvier located every 1-2 mm allow for depolarization, transmission of AP is faster in myelinated axons
RMP
Rest membrane potential
What does RMP result from?
a difference in charge across the cell membrane
What is the charge in the inside and outside of the cell membrane?
Inside of the membrane is negative relative to the outside (positive)
What is the average RMP in a nerve cell?
-70 to -90 mV
The inside and outside of the cell are ____?
electroneutral
What are three factors that maintain the RMP?
- selective permeability (passive based diffusion)
- Na+/K+ pump
- large anions trapped on the inner surface of the membrane
How many Na+ and K+ can use the Na+/K+ pump at a time?
3 Na+ out 2K+ in
What is selective permeability in the maintenance of RMP?
Passive leakage of ions through channels by a concentration gradient
What is RMP permeable to?
K+ barely permeable to Na+ Ca2+ and Cl-
Does the ion pump go against or with the concentration gradient?
It goes against the concentration gradient and for Na+ it pumps it against the membrane polarity
How much ATP availability does the Na+/K+ pump require?
40% of ATP availability
What are excitable cells?
cells that can generate AP, need to be stimulated
How are excitable cells stimulated?
through chemical, electrical or physical stimulations that induce threshold
What does threshold induce?
opening of voltage-gated ion channels
What is depolarization?
If Na+ channels open Na+ rushes inside the cells (gradient concentration)
What is repolarization?
subsequent opening of K+ channels results in outflow of K+ returning the potential to RMP
What are the steps to generating action potential in neurons?
- initial depolarization (stimulation) needs to reach threshold to provoke the opening of Na+ voltage-gated channels - depolarization
- after about 0.5 ms, opened Na+ channels close rapidly
- K+ voltage-gated channels then open (delayed compared to Na+ channels) which results in an outflow of K+ - repolarization
- K+ voltage-gated channels then progressively close, outflow of K+ continues after reaching RMP - hyperpolarization
- once all gated channels are closed ions rejoin their respective compartments by diffusion of Na+/K+ pumps
- neurons cannot be re-stimulated until RMP restored (refractory period)
What are the two types of ion-gated channels?
voltage-gated channels and ligand-gates channels (neurotransmitter binding sites)
What is the all-or-none rule?
when threshold is met an AP is generated, the amplitude of the AP is fixed for that cell. The intensity of the effect is caused by multiple firing of AP (frequency) not the strength
Describe the conduction of AP in an unmyelinated axon
depolarization and repolarization processes propagate along the cell membrane, need for the change in potential to reach threshold on the nearby microdomain to trigger opening of gated channels
Describe the conduction of AP in a myelinated axon
AP occurs the same way as an unmyelinated axon except only at the nodes of ranvier, current jumps from node to node
Does the velocity of AP increase in myelinated axons or unmyelinated axons?
Myelinated axons have an increase AP conduction velocity as there is less energy required to transport the ions
What are some factors that affect nerve velocity?
thickness of myeline
diameter of fiber (thicker=faster)
What is saltatory conduction?
myelinated AP conduction
What does myelinated AP conduction prevent?
leakage of ions
What is synaptic transmission?
continuity of a signal between neuron and other neurons or between neuron and target cells
What is the cell membrane of an axon terminal made of?
phospholipids (electric insulator)
What is the synaptic cleft?
gap between the pre-post synaptic cell
What is the difference between electrical and chemical synapses?
Electrical - no gap between two cells
Chemical - gap to transmit signal chemical through neurotransmitter
What is a neurotransmitter?
molecule able to transmit information from a neuron to convert the signal (AP) into a chemical signal
they:
are released by pre-synaptic neurons into the cleft
bind to specific receptors on the postsynaptic membrane and elicit a response
How are neurotransmitters classified?
Small molecules: AA derivatives, synthesized in nerve terminals
Neuropeptides (3-40 AA): synthesized in cell body, packaged in secretory vesicles, transported at site of release
What are the neurotransmitters for the sympathetic and the parasympathetic NS
Sympathetic - adrenaline/noradrenaline
Parasympathetic - ACh
What is common in neuromuscular synapses?
postsynaptic folding
What is the neuromuscular synapse transmitter?
ACh
What are the steps of the synapse?
- AP
- AP opens voltage-gated Ca2+ channels = in-flux of Ca2+
- Ca2+ triggers exocytosis
- Diffusion in the cleft
- Binding to specific receptors
- Ion channels open on post-synaptic membrane = depolarization
- Neurotransmitter inactivated termination of signal
How is termination of transmission done in small molecules?
Picked back up by presynaptic neuron via endocytosis and recycled
OR
deactivated in the cleft by enzymes released by postsynaptic cell (acetylcholine esterase)
receptor can be desensitized
How is termination of transmission done in neuropeptides?
after binding to its receptor, can be internalized by post-synaptic cell via endocytosis and be degraded by cellular enzymes, broken down by extracellular peptidase in gap
receptor can be desensitized
In the case of neuromuscular synapse, what happens to the muscle cell?
1 neuron to depolarize 1 muscle cell
In the case of neuron-neuron synapse, how many other neurons can transmit an impulse to one neuron?
1 neuron can receive impulses from multiple other neurons, one impulse does not always lead to a response
What is an excitatory synapse?
depolarization - entry of Na+
What is an inhibitory synapse?
hyperpolarization - entry of Cl= and/or outflow of K+
What are the four parts of the brain?
Cerebrum (forebrain)
Diencephalon (thalamus and hypothalamus)
Cerebellum
Brain stem
What are the three parts of the brainstem?
Mesencephalon, Pons and medulla oblongata
What are the functions of the CNS?
- Receives continuous flow of information (outside/inside)
- analyzes and interprets the information
- sends commands to the body to maintain function vital systems and organs and respond to external environment
What are the meninges?
3 layers surrounding the brain and spinal cord
- dura mater (thick/tough) outside layer
supports brain, inserted between cerebral hemispheres
- arachnoid mater
- sub-arachnoid space (filled with CSF) between the arachnoid mater and pia mater
- pia mater (tightly attached to neural tissue
What is the venous sinus formed by and what is its function?
formed by the dura mater, collects most of the blood and CSF from the brain
What is CSF formed by?
choroid plexus: capillaries of specialized areas of pia mater
Where is the CSF circulated?
from the brains ventricles down to the central canal of the spinal cord, it diffuses from 4th ventricle to the subarachnoid space and circulates around the brain and the spinal cord, it is then drained into the venous sinus before entering blood circulation
What are the 4 roles of the CSF
- provides nutrients to CNS
- protection shock absorber
- ionic concentration ideal for optimum neuronal function
- blood-CSF barrier: at choroid plexus, uptake of nutrients and drugs into CSF
What does the blood-brain barrier allow to pass?
no cells or proteins, only low AA, liposoluble substances such as gases
What is the cerebral cortex?
part of the cerebrum
it is all grey matter
most superficial layer of the brain and is responsible for the conscious experience of sensory input, site of high nervous association, educatable, different parts within cerebral cortex
What are two other parts of the cerebrum?
somatosensory cortex and the motor cortex
What does the white matter beneath the cortex include?
association fibers between parts of the cortex
commissural fibers between the two hemispheres
projection fibers that connect cortex to other brain structures and spinal cord
Where are the basal nuclei located?
deep within the cerebrum (close to thalamus)
What is the basal nuclei composed of?
paired nuclei composed of large pools of neurons
What is the function of basal nuclei?
Control complex semi-voluntary movements (walking/running)
work in conjunction with the cortex and the cerebellum
What is the function of the cerebellum?
- receives information from the inner ear (equilibrium) proprioceptive receptors (muscles, tendons, joints) and cortex (visual and motor)
- main role is to prevent distortion of intended movement
- receives info regarding the status of the body, intended movement, makes adjustment for a smooth completion
- corrective signals sent via thalamus to cortex and spinal nuclei commanding the muscles
Which animals is the cerebellum well developed?
animals requiring precise adjustment for locomotion (air ground water)
What is the function of the diencephalon?
inter brain (hypothalamus/thalamus)
thalamus is a relay station for sensory information, cerebellum and basal ganglia and the cerebral cortex
epithalamus contains olfactory correlation center and the pineal gland
hypothalamus produces neuropeptides that control the anterior pituitary
produce neurohormones released by post pit
regulator of the ANS, with the brain stem, controls homeostasis
What does the brain stem contain?
nuclei that govern body function by reflexes, also contains large amounts of white matter (conveyors)
What is the function of the mesencephalon?
- visual reflex center, receives visual info, controls eye movement
- auditory reflex center, turns head for noise
Which animal has a very well developed mesencephalon?
birds, most mammals midbrain is very small
What is the function of the pons and the medulla oblongata?
postural reflex center
control respiratory movements
medulla oblongata: heart activity, blood pressure and relative dist of blood to organ control
How many cranial nerve pairs are there?
12
What nerve is the 10th?
X - vagus nerve, most widely distributed nerve throughout the body (from neck to abdomen), contains parasympathetic fibers to visceral structures in the thorax and abdomen
What are the 5 regions of the spinal cord?
cervical, thoracic, lumbar, sacral and coccygeal
Label the parts of the cross section of the spinal cord
refer to slides
What is the white matter in the spinal cord arranged by?
columns
What is the function of the grey matter in the spinal cord?
dorsal horm - sensory
ventral horm - motor (skeletal muscles) and autonomic fibers
middle zone - association
How are the spinal nerves joined?
by the dorsal and ventral roots, which merge within spinal canal
What is the number of spinal nerves relative to?
The number of vertebra
What are the three levels of control of movement in the CNS
Higher centers (cerebral cortex (conscious)
Middle level
- sensorimotor cortex
- cerebellum
- basal ganglia (semi-voluntary movements)
Lower level - spinal cord from which motor neurons exit (somatic reflex arcs)
What is proprioception?
Ability to sense movement and location. e.g. Tensions in muscles and tendons, and angles of joints send back sensory information to CNS
Where do somatic reflex arcs occur?
spinal cord
What is a reflex?
automatic or unconscious response of effector organs to a stimulus
What are the five fundamental components of a reflex?
- sensory cells/receptors
- sensory nerve fibers
- CNS
- motor nerve fibers
- effectors
What are the components of a somatic muscle reflex arc?
- receptors
- transduce environmental energy (skin, muscle, tendon)
- convert energy into AP - sensory (afferent) nerve
- conduct AP from the receptor
- cell body in ganglion outside of spinal cord
- enter spinal cord via dorsal roots - coordinating center
- monosynaptic
- multisynaptic (elaborate reflexes) - motor (efferent) nerve
- carries APs from CNS to target organs
- via ventral roots
- cell body within the CNS - target organ response
- skeletal muscle reflex
- multiple targets (e.g. scratching)
What is the muscle stretch detected by in the stretch and tendon reflex?
muscle spindles
How do muscle stretching reflexes work?
middle segment acts as stretch receptor by pinching the bear end of the sensory neuron which travels to spinal cord, sensory nerve maes excitatory synaptic contact with motor neurons serving the same muscle which results in muscle shortening
What are changes in tendon length detected by?
golgi organ
How does the tendon reflex work?
muscle contracts, pulls tendon, squeezes bare end of neuron, sensory nerve contacts with an inhibitory interneuron in spinal cord, inhibits motor neurons serving the same muscle
What is the knee-jerk reflex?
same protective reflex concept to prevent tendon injury
What are the functions of the autonomous nervous system?
- autonomic - controls body function without conscious thought (homeostasis, accomplishes by autonomic reflexes)
- controls smooth muscle, cardiac muscle and glands
(resp, heart rate, blood pressure, digestion, rumination, sleep, arousal, body temperature)
What are the steps to an autonomic reflex?
- sensory cells: depend on system
- sensory nerve fibers: no major difference from - somatic arcs
- integration center:
- hypothalamus: master
- brain stem: respiration
- spinal cord: local integration in thoracic and sacral segments
- receive continuous info from sensory nerves - motor nerve fiber
- target organ (smooth muscle, cardiac muscle, glands)
- two peripheral nerves
- preganglionic neuron and post ganglionic neuron
- cell body of the post ganglionic neuron is in a ganglion - effectors
What is the ANS mainly controlled by?
negative feedback
What are the three divisions of the ANS
- sympathetic
- parasympathetic
- enteric (associated with parasympathetic)
When is the sympathetic system activated?
during stress
When is the parasympathetic system active?
most active during rest
What is the difference between the sympathetic and the parasympathetic systems in terms of ganglionic nerves?
Sympathetic: preganglionic neurons originate in tharacic or lumbar spinal area and send axons to sympathetic ganglia which from a chain parallel to the spinal cord (lots of communication) (short pre, long post)
Paraympathetic: preganglionic neurons originate in the brain or sacral part of the spinal cord and send axons to ganglia near or within effector organs (long pre, short post)
What is the long chain that the sympathetic pre ganglionic neurons connect by?
paravertebral sympathetic ganglion chain
What is a special feature of the preganglionic neurons in the sympathetic system?
some preganglionic fibers extend to the adrenal medulla to stimulate the secretion of epinephrine and norepinephrine
Where are the ganglia located in the parasympathetic nervous system?
in the wall or adacent to target organs, no interconnection between ganglia
What is a special feature of the postganglionic cells in the parasympathetic system
very short, no branching off, with direct connection with specific organs, no enhancement by hormones
What are the two receptors of ACh
Nicotinic and muscarinic
What are some features of nicotinic receptors for ACh?
- preganglionic synapses
- neuromuscular junctions
- ionotropic (part of an ion channel)
What are some features of muscarinic receptors for ACh?
- in target organs for parasympathetic
- requires intracellular second messengers to activate target cell
- effect can be stimulatory or inhibitory
- slower and more prolonged effect than nicotinic
What are the receptors for (nor)adrenalin
- alpha-adrenergic
- alpha1 = more Ca2+
- alpha2 = less cAMP
- usually constriction of smooth muscles (vascular)
- beta-adrenergic
- beta1 and beta2 = more cAMP
- main form in heart increases contraction strength and rate
- relaxation of smooth muscles
What receptor blocker would you use for hypertension?
beta-adrenergic blocker (propranolol) - decreases heart rate (beta1)
What receptor blocker would you use for asthma?
beta2-adrenergic agonist (salbutamol) - brochodilation
What is the function of atropine?
muscarinic receptor blocker
drop in eye - dilation of pupils
inhibits contraction of lower GI tract
reduces mucus production in respiratory tract
