BIO 168 Ch. 11, 12, 13, & 14 exam

Nervous System

Controls and communicates with the rest of the body. 3 major functions:

1. Sensory input: Information gathered by sensory receptors about internal and external changes

2. Integration: Processing and interpretation of sensory input

3. Motor output: Response initiated by activating effector organs (muscles and glands)

Central Nervous System (CNS)

• Brain and spinal cord of dorsal body cavity

• Integration and control center

• Interprets sensory input and dictates motor output

Peripheral Nervous System (PNS)

The portion of nervous system outside CNS. Consists mainly of nerves that extend from brain and spinal cord

• Spinal nerves to and from spinal cord

• Cranial nerves to and from brain

• Enteric nervous system (walls of gastrointestinal tract)

• Two divisions: Sensory and Motor

PNS: Motor (Efferent) Division

Transmits impluses from CNS to effectors (muscles and glands)

Two divisions: Somatic NS and Autonomic NS

PNS: Sensory (Afferent) Division

Somatic sensory fibers: convey impulses from skin, sk muscles, and joints to CNS

Visceral sensory fibers: convey impulses from visceral organs to CNS

PNS Motor division: Somatic Nervous System

• Somatic nerve fibers conduct impulses from CNS to skeletal muscle

• Conscious control of skeletal muscle

PNS Motor division: Autonomic nervous system (ANS)

• Consists of visceral motor nerve fibers

• Regulates smooth muscle, cardiac muscle, and glands

• Two functional subdivisions work in opposition of each other: Sympathetic and Parasympathetic divisions

PNS → Motor div. → ANS: Sympathetic division

Mobilizes body systems during activity (fight or flight)

PNS → Motor div. → ANS: Parasympathetic division

• Conserves energy

• Promotes housekeeping functions during rest

• Rest and digest

Nervous tissue consists of two cell types…

Neuroglia (glial cells) and Neurons (nerve cells)

Neuroglia (glial cells)

Smalls cells that surround and wrap delicate neurons. 4 main types:

• Astrocytes

• Microglial cells

• Ependymal cells

• Oligodendrocytes

Neuroglia: Astrocytes

Most abundant and versatile. Cling to neurons, synaptic endings and capillaries

• Support and brace neurons

• Help with exchanges between capillaries and neurons (waste and nutrients)

• Guide migration of young neurons

Neuroglia: Microglial cells

• Small ovoid cells with thorny processes that touch and monitor neurons

• Migrate toward injured cells (defensive)

• Can transform to phagocytize microorganisms and neuronal debris

Neuroglia: Ependymal cells

• Range in shape from squamous to columnar (may be ciliated to circulate CSF)

• Line the central cavities of the brain and spinal cord

• Form permeable barrier between cerebrospinal fluid (CSF) in cavities and tissue fluid bathing CNS cells

Neuroglia: Oligodendrocytes

• Branched cells with fewer processes than astrocytes

• Processes wrap CNS nerve fibers forming insulating myelin sheath

PNS Neuroglia: Satellite cells

• Surround neuron cell bodies in PNS

• Function similar to astrocytes of CNS

PNS Neuroglia: Schwann cells/neurolemmocytes

• Surround all peripheral nerve fibers and form myelin sheaths around the thicker nerve fibers

• Function similar to oligodendrocytes

• Vital to regeneration of damaged peripheral nerve fibers

Neurons/nerve cells

Structural units of nervous system. Large, highly specialized cells that conduct impulses

• Extreme longevity (lasts a lifetime)

• Amitotic

• High metabolic rate and require continuous supply of oxygen and glucose

• All have a cell body and one or more slender processes

Neuron cell body/soma

Receptive region that receives info from other neurons

• Has nucleus and nucleolus

• Rough ER (chromatophilic substance)

• Biosynthetic and metabolic center

• Maintains shape with microtubules and neurofilaments

Nuclei

Clusters of neuron cell bodies in CNS

Ganglia

Clusters of neuron cell bodies in PNS

Dendrites

Motor neurons contain hundreds of these branches. Contain same organelles of cell body

• Receptive (input) regions of neuron

• Convey incoming messages to cell body as graded potentials (short-distance signals)

• Finer ones can be highly specialized

Axon

• Conducting region of neuron (nerve impulses) and releases neurotransmitters

• Starts at Axon hillock (cone shaped area), then initial segment

• Have branches called axon collaterals and end bulbs called terminal branches

Myelin Sheath

White, fatty substance that coats many axons, particularily ling or large axons

• Protect and electrically insulate axons

• Increase speed of nerve impulse transmission

Nodes of Ranvier

Myelin sheath gaps

• Gaps between adjacent schwann cells

• Sites where axon collaterals can emerge

• Occur between adjcant Schwann cells (PNS) or Oligodendrocyte processes (CNS)

Sensory (afferent) neurons

• Transmit impulses from sensory receptors toward CNS

• Almost all are unipolar neurons

• Cell bodies located in ganglia in PNS

Motor (efferent) neurons

• Carry impulses from CNS to effectors

• Multipolar neurons

• Most cell bodies located in CNS (except some autonomic neurons)

Interneurons

• Lie between motor and sensory neurons in neural pathways

• Shuttle signals through CNS pathways, most are entirely within CNS

• 99% of body’s neurons are interneurons

Resting Membrane Potential (RMP)

A typical neuron has a resting membrane potential of approximately -70mV. This means the inside of the cell is -70mV more negative than the outside. This stable voltage is primarily maintained by the sodium-potassium pump, selective membrane permeability, and the electrical/chemical gradients of specific ions.

Voltage

A measure of potential energy generated by separated charge

• Measure between two points in volts (V) or millivolts (mV)

• Called potential differences

• Charge different across plasma membrane results in potential

• Greater charge different between points = higher voltage

Current

Flow of electrical charge (ions) between two points

• Can be used to do work

• Flow is independent on voltage and resistance

Resistance

Hindrance to charge flow

• Insulator: susbtance with high electrical resistance

• Conductor: substance with low electrical resistance

Ohm’s Law

Gives relationship of voltage, current, resistance

Current (I) = Voltage (V) / Resistance (R)

Chemically gated channels/ Ligand-gated channels

Open only with binding of a specific chemical (ex. neurotransmitter)

Voltage-gated channels

Open and close in response to changes in membrane potential

Mechanically gated channels

Open and close in response to physical deformation of receptors, as in sensory receptors

Electrochemical gradient

• Concentration gradient: ions move from area of H to L concentration

• Electrical gradient: ions move toward area of opposite electrical charge

Changing the RMP

• Concentrations of ions across membrane change

• Membrane permeability to ions changes

• These changes produce two types of signals to receive, integrate, and send information: Graded and Action Potentials

Graded Potentials

Incoming signals operating over short distances. Important to initiate APs

• Voltage varies directly with stimulus strength. Stronger stimulus = larger change in MP

• Decay quickly due to leak channels that allow ions to escape

Actions Potentials

Long distance signals of axons

• Occur only in excitable membranes: neurons (nerve impulses) and muscle cells

• They do not decay due to regeneration

• Involve specific voltage-gated channels

Define: Depolarization

Decrease in membrane potential (moves toward zero and above)

Define: Hyperpolarization

Increase in membrane potential (more negative)

Graded potentials: Receptor/Generated Potential

Graded potentials in receptors of sensory neurons

Graded potentials: Postsynaptic Potential

Produced in a neuron that is stimulated by neurotransmitter released from another neuron

Graded potentials: End-plate potential

Special type of graded potential that occurs in muscle cell, instead of postsynaptic neuron, triggering AP for muscle contraction

Generation of an AP: 1. Resting state

No ions move through voltage gated channels

Generation of an AP: 2. Depolarization

Caused by Na+ flowing into the cell

Generation of an AP: 3. Repolarization

Caused by K+ flowing out of the cell

Generation of an AP: 4. Hyperpolarization

Caused by K+ continuing to leave the cell

Threshold

Must be reached for axon to fire/ depolarization

• Membrane is depolarized by 15 to 20 mV

• Na+ permeability increases and Na+ influx exceeds K+ efflux

• All or none phenomenon: AP either happens completely or does not happen at all

Propagation

Allows AP to be transmitted from origin down entire axon length

The stronger the stimulus, the more _______ APs are generated

frequently

Refractory period

Time in which neuron cannot trigger another AP. Na+ channels are open, so neuron cannot respond to stimulus

• Absolute: ensures that each AP is all or none event. Enforces one way transmission of APs

• Relative: Follows absolute period. Threshold for AP generation is elevated so only strong stimulus can stimulate an AP

Conduction velocity

Rate of AP propagation depends on two factors:

• Axon diameter: larger diamter fibers have less resistance to local current flow, so have faster impulse conduction

• Degree of myelination: If myelinated, saltory conduction occurs which is very fast. APs are generated at sheath gaps due to presence of voltage gated Na+ channels. If not myelinated, then conduction is slow

Synapse

Junctions that mediate information transfer to another neuron or effector

Two types: electrical and chemical

Presynaptic neuron

Neuron conducting impulses toward synapse (sends information)

Postsynaptic neuron

Neuron transmitting electrical signal away from synapse (receives info). In PNS, may be a neuron, muscle cell, or gland cell

Synaptic connections

• Axodendritic synapses: between axon terminals of one neuron and dendrites of others

• Axosomatic synapses: between axon terminals of one neuron and soma (cell body) of others

Less common synaptic connections

• Axoaxonal (axon to axon)

• Dendrodendritic (dendrite to dendrite)

• Somatodendritic (cell body to dendrite)

Electrical synapses

• Less common, joined by gap junctions that connect cytoplasm of adjacent neurons

• Communication is rapid and multidirectional

• Found in some brain regions responsible for eye movements or in hippocampus

• Most abundant in embryonic tissue

Chemical synapses

• Most common type

• Release and reception of neurotransmitters

• Axon terminal contains synaptic vesicles with neurotransmitter

• Receptor region: receives neurotransmitter

• Both parts separated by synaptic cleft

Information transfer across chemical synapses

1. AP arrives at the axon terminal of presynaptic neuron

2. Calcium ions enter the axon terminal through voltage-gated channels

3. Influx of calcium ions causes the release of neurotransmitter from the axon terminal

4. Neurotransmitter diffuses across the synaptic cleft and binds to receptors on the postsynaptic membrane

5. Chemically gated channels open, resulting in graded potentials

6. Neurotransmitter effects are terminated (reuptake, enzyme degradation, diffusion away)

Synaptic delay

Rate-limiting step of neural transmission. Slows down quick AP transmission

Neurotransmitters

Chemical messengers released by neurons to inhibit or excite

Acetylcholine (ACh)

• Released at NMJs, also used by many ANS and some CNS neurons

Biogenic amines

• Catecholamines: Epinephrine, Norepinephrine, Dopamine

• Indolamines: Serotonin & Histamine

All widely used in brain: play roles in emotional behaviors

Used by some ANS motor neurons especially NE and Epi

Imbalances associated with mental illness

Amino acids

• Glutamate

• Aspartate

• Glycine

Peptides

Strings of amino acids that have diverse functions

• Substance P: mediator of pain signals

• Endorphins: act as natural opiates, reduce pain perception

• Gut brain peptides: somatostatin and CCK

Purines

Monomers of nucleic acids that have an effect in both CNS and PNS

• ATP - energy

• Adenosine: a part of ATP is a potent inhibitor

Gases and Lipids

• Nitric oxide (NO), Carbon monoxide (CO), hydrogen sulfide (H2S) gases

• Bind with G protein-coupled receptors in brain

Endocannaboids

Act as same receptors as THC (marijuana)

Most common G protein linked receptors in brain

Believed to be involved in learning and memory

Channel linked receptors

• Ligand-gated ion channels

• Action is immediate and brief

• Excitatory receptors are channels for small cations

• Used by glutamate, GABA, Glycine, ACh, Serotonin

G Protein Linked receptors

• Responses are indirect, complex, and slow

• Involves transmembrane protein complexes

• Used by ACh, Biogenic amines, Neuropeptides

• Cascade

Cephalization

• Evolutionary development of rostral (anterior) portion of CNS

• Resulted in increased number of neurons

• Highest level reached in human brain

Gray matter

Short, nonmyelinated neurons and cell bodies

Surrounded by white matter

White matter

Myelinated and non myelinated axons

Surrounds gray matter

4 Brain regions

1. Cerebrum

2. Diencephalon

3. Brain Stem (midbrain, pons, medulla oblongata)

4. Cerebellum

Why is it better for the brain to have convolutions instead of a smooth cerebral surface?

It increases the surface area of the cerebral cortex

Ventricles

• CSF Fluid filled chambers continuous to one another and central canal of spinal cord

• Lined by ependymal cells

• Paired lateral ventricles are large and each one is connected to the third ventricle via interventricular foramen

• Third ventricle is connected to the 4th ventricle via cerebral aqueduct

• 3 openings connect 4th ventricle to subarachnoid space

Gyri

ridges

Sulci

Shallow grooves

Fissures

Deep grooves

Several sulci divide each hemisphere into 5 lobes

• Frontal lobe

• Parietal lobe

• Temporal lobe

• Occipital lobe

• Insula

Major sulci that divide lobes:

• Central sulcus: separates precentral gyrus of frontal lobe and postcentral gyrus of parietal lobe'

• Parieto-occipital sulcus: separates occipital and parietal lobes

• Lateral sulcus: outlines temporal lobes

Each hemisphere has 3 basic regions:

• Cerebral cortex: gray matter superficially. Executive suite of brain: conscious mind (awareness, sensory, vol. motor, communication, memory, and understanding

• Internal white matter

• Basal nuclei deep within white matter

Motor areas

Control voluntary movement

• Primary (somatic) motor cortex: conscious control of precise skeletal muscle movements

• Premotor cortex: Helps plan movements

• Broca’s area: directs muscles of speech production

• Frontal eye field: controls voluntary eye movements

Sensory areas

Conscious awareness of sensation

• Primary somatosensory cortex: receives general sensory info from skin and proprioceptors of sk muscle, joints, and tendons

• Somatosensory association cortex: Integrates sensory input from primary somatosensory cortex for understandinf object (size, texture, etc.)

• Primary visual area: receives visual info from retinas

• Visual association area: uses past visual exp to interpret visual stimuli

• Primary auditory cortex: Interprets info from inner ear as pitch, loudness, and location

• Auditory association area: stores memories of sounds abd permits perception of sound stimulus

• Vestibular cortex: conscious awareness of balance

• Primary olfactory cortex: awareness of odors

• Gustatory cortex: perception of taste

• Visceral sensory area: visceral sensations like upset stomach or full bladder

Association areas

Receive inputs from multiple sensory areas and send outputs to multiple areas

• Anterior association area: involves with intellect, cognition, recall, and personality

• Posterior association area: plays roles in recognizing patterns and faces and localizing us in space + involved in understanding written and spoken language (Wernicke’s area)