1. The Spinal Cord has a central cavity surrounded by a grey matter core
2. External to which is white matter composed of myelinated fiber tracts
3. Similar to spinal cord but with additional areas of gray matter and outer cortex of gray matter
4. The four major parts of the brain are the, cerebral hemispheres, diencephalon, cerebellum, brain stem
Cerebrum
5. The cerebrum is also known as the...cerebral hemispheres
6. The cerebrum has three basic regions: cortex, white matter, and basal nuclei
The cortex
7. The cortex is comprised of superficial gray matter; accounts for 40% of the mass of the brain
8. The cerebral cortex enables what things? sensation, communication, memory, understanding,
9. The cerebral cortex has what general areas...motor areas, sensory areas, and association areas
10. Left hemisphere – controls language, math, and logic
11. Right hemisphere – controls visual-spatial skills, emotion, and artistic skills
12. The cerebral white matter consists of myelinated fibers and their tracts.
13. The cerebral white matter is responsible for communication between: cerebral cortex and lower CNS
center, and between areas of the cortex
Cerebral White Matter Types:
1. Commissures – connect corresponding gray areas of the two hemispheres
2. Association fibers – connect different parts of the same hemisphere
3. Projection fibers – enter the hemispheres from lower brain or cord centers
Basal Nuclei
1. The basal nuclei part of the nervous system is comprised of: Masses of gray matter found deep within the
cortical white matter of the cerebral hemispheres
2. The two parts of the basal nuclei are the caudate nucleus and the lentiform nucleus
3. Disorders of the basal nuclei include what two dz’s? Huntingtons, and parkinson’s
4. The basal nuclei controls what two things: Motor control (muscular activity) and regulate attention and
cognition
Diencephalon:
1. Comprised of what three parts? (Thalamus, hypothalamus, epithalamus)
2. Encloses what ventricle? 3rd
Thalamus:
1. Paired, egg-shaped masses containing four groups of nuclei that project to and receive fibers from the
cerebral cortex
2. Acts as a “Relay Station” for information entering the brain
3. Plays a key role in mediating sensation, motor activities, cortical arousal, learning, and memory
Hypothalamus
1. Infundibulum – stalk of the hypothalamus; connects to the pituitary gland
2. Functions: Regulates blood pressure, rate and force of heartbeat, digestive tract motility, rate and depth of
breathing, and many other visceral activities
3. Is involved with perception of pleasure, fear, and rage
4. Controls mechanisms needed to maintain normal body temperature
5. Regulates feelings of hunger and satiety
6. Regulates sleep and the sleep cycle
Epithalamus
1.Most dorsal portion of the diencephalon
2. Pineal gland – extends from the posterior border and secretes melatonin- hormone involved with sleep
regulation, sleep-wake cycles, and mood
Brainstem:
1. Consists of what three regions? Midbrain, pons, medulla oblongata
2. Similar to spinal cord but contains embedded nuclei
3. Controls automatic behaviors necessary for survival Exs: Heart rate, respiratory rate
4. Provides the pathway for tracts between higher and lower brain centers
Cerebellum
1. Located dorsal to the pons and medulla
2. Makes up 11% of the brain’s mass
3. Provides precise timing and appropriate patterns of skeletal muscle contraction, ie. coordinates
movements
4. Cerebellar activity occurs subconsciously
The four ventricles of the brain
1. There are two C-shaped lateral ventricles
2. The 3rd is found in the diencephalon
3. the fourth is dorsal to the pons
Protection of the brain
1. The brain is protected by three things: bone, meninges, and cerebrospinal fluid
Meninges
1. Three connective tissue membranes lie external to the CNS – they are: dura mater, arachnoid mater, and
pia mater
2. Major functions are to Cover and protect the CNS,Protect blood vessels, Contain cerebrospinal fluid
(CSF) (b/t arachnoid and pia)
Blood-Brain Barrier
1. Protective mechanism that helps maintain a stable environment for the brain
2. Selective barrier that allows nutrients to pass freely
3. Bloodborne substances are separated from neurons by what 3 things:
--endothelium of capillary walls
--thick basal lamina
--bulbous “feet” of astrocytes
Spinal Cord
1. Protected by what three things? bone, meninges, and CSF
2. Epidural space – space between the vertebrae and the dural sheath (dura mater) filled with fat and a
network of veins
3. Cervical and lumbar enlargements – sites where nerves serving the upper and lower limbs emerge
Gray Matter and Spinal Roots
1. Gray matter consists of three things:somas, unmyelinated processes, and neuroglia
2. Dorsal segment ( dorsal horns )– sensory
--Afferent fibers from sensory neurons form dorsal roots
--Sensory neuron somas found in dorsal root ganglia (PNS)
3. Ventral segment (ventral horns )– motor
--Axons of motor neurons leave spinal cord through venral roots
4. Dorsal and ventral roots fuse laterally to form spinal nerves
White Matter in the Spinal Cord
1. Fibers (axons) run in three directions – ascending, descending, and transversely
2. Fiber tracts are composed of axons with similar functions
3. Ascending tracts send impulses to the sensory cortex
4. Descending tracts send impulses that ultimately control muscles and visceral organs
PNS
General:
1. Changes in membrane potential are signals used by neurons (and muscle cells) to send, receive, or
integrate information.
--Changes in membrane potential that occur in neurons and other excitable cells are mainly produced by
changes in membrane permeability to ions through channels that occur in response to:
-neurotransmitter release
-change in membrane potential
-pharmacological agents/toxins
Types of membrane potential changes that occur:
Depolarization – the inside of the membrane becomes less negative
Repolarization – the membrane returns to its resting membrane potential
Hyperpolarization – the inside of the membrane becomes more negative than the resting potential
Graded Potentials
1. Sufficiently strong graded potentials can initiate action potentials
2. Their magnitude varies directly with the strength of the stimulus
3. Short-lived, local changes in membrane potential-can only travel over short distances
Action potentials
1. A rapid reversal of membrane potential above a threshold level with a total amplitude of ~100 mV
2. Action potentials are only generated by muscle cells and neurons
3. They do not decrease in strength over distance
4. They are the principal means of neural communication
5. An action potential in the axon of a neuron is often called a nerve impulse
Conduction Velocities of Axons
1. Conduction velocities vary widely among neurons
2. Current passes through a myelinated axon only at the nodes of Ranvier (salutatory conduction)
3. Axon diameter – the larger the diameter, the faster the impulse
Multiple Sclerosis (MS)
1. myelin sheaths in the CNS become nonfunctional scleroses and nerve fibers degenerate
Synapses
1. Junctions that mediate information transfer from one neuron to what two things? To another neuron
To an effector cell
Types of Synapses (functional classification)
Electrical synapses:
--Less common than chemical synapses
--Made of gap junctions - ions pass directly from one neuron to another
Chemical Synapses:
1. Specialized for the release and reception of neurotransmitters
2. Typically composed of two parts: Axonal terminal and Receptor region
Transmission across the synaptic cleft:
1. Is a chemical event (as opposed to an electrical one)
2. Ensures unidirectional communication between neurons
Termination of Neurotransmitter Effects
1. Removal of neurotransmitters occurs when they:
--Are degraded by enzymes
--Are reabsorbed by astrocytes or the presynaptic terminals
--Diffuse away from the synaptic cleft
2. Synaptic delay is the rate-limiting step of neuronal transmission
Neurotransmitters and their Receptors
1. 50 different neurotransmitters have been identified
2. Classified chemically and functionally
Neurotransmitters: Acetylcholine
1. Released at the neuromuscular junction
2. Synthesized and enclosed in synaptic vesicles
3. Degraded by the enzyme acetylcholinesterase (AChE)
4. Released by:
--All neurons that stimulate skeletal muscle NMJs
--Some neurons in the autonomic nervous system
Neurotransmitters: Biogenic Amines
1. Includes:
--Catecholamines – Dopamine, norepinephrine (NE), and epinephrine.
--Indolamines – serotonin and histamine.
2. Broadly distributed in the brain
3. Play roles in emotional behaviors and our biological clock
Synthesis of Catecholamines
1. Norepinephrine and dopamine are synthesized in axonal
terminals
2. Epinephrine is released by the adrenal medulla
Neurotransmitters: Amino Acids
1. Includes:
- GABA (gamma amino butyric acid)
- glycine
- aspartate
- glutamate
2. Found only in the CNS
Neurotransmitters: Peptides
1. Includes:
- Substance P – mediator of pain signals.
- Beta endorphin, and enkephalin
2. Act as natural opiates, reducing our perception of pain
3. Bind to the same receptors as opiates and morphine
Functional Classification of Neurotransmitters
1. Two classifications:
--Excitatory neurotransmitters cause Depolarization.
(e.g., glutamate)
--Inhibitory neurotransmitters cause hyperpolarization.
(e.g., GABA and glycine)
More negative than the resting membrane potential. Less likely to undergo AP.
2. Some neurotransmitters have both excitatory and inhibitory effects
--Determined by the receptor type of the postsynaptic neuron
--Example: acetylcholine
3. acetylcholine
--Excitatory at neuromuscular junctions with skeletal muscle
--Inhibitory in cardiac muscle
Neurotransmitter Receptor Mechanisms
1. Direct: neurotransmitters that open ion channels
--Promote rapid responses
--Examples: ACh and amino acids
2. Indirect: neurotransmitters that act through second messengers. (ANS).
--Slower onset of response; promote longer-lasting effects
--Examples: biogenic amines, peptides, and dissolved gases
--Many are G-protein-linked receptor mediated