Chapter 34

Neural Control- A Summary

AP BiologySpring 2011

Nervous System

Nervous System Sensory Neurons: detect information about

stimuli, such as light Interneurons: accept the senosory input,

process it, and signal other neurons Motor Neurons: relay new signals to

effectors- muscles and glands- that carry out responses Neuroglia: structurally and metabolically support the neurons

Invertebrate Nervous System Cnidarians: jellyfish, radial body plan

Two epithelial tissues: an epidermis and gastrodermis

Nerve net: asymmetrical mesh of neurons, controls simple movement of both

Motor neurons activate epithelial cells that have long contractile extensions, by making them contract the nerve net changes diameter of mouth or body or bends tentacles

Invertebrate Nervous System Bilateral animals

Ex. Flatworm Bilateral nervous system: have nerves,

branching nerves join two nerve cords in a ladder-like array

Invertebrate Nervous System Ganglion: cluster of nerve cell bodies that

function as a local integrating center Cephalization: formation of a head evolved

with bilateral nervous systems

Ganglion Ganglion

Vertebrate Nervous System Two functional divisions:

Central Nervous System (CNS): brain and spinal cord

Peripheral Nervous System (PNS): nerves extending through the rest of the body

Invertebrate Nervous System Afferent: deliver signals into the central

system PNS

Efferent: carry signals out of it Motor fibers

Outline of Peripheral Nervous System Somatic System: controls the voluntary

muscles Autonomic System: controls involuntary

muscles Sympathetic: fight or flight response, increase

heart and breathing rate, liver converts glycogen to glucose, bronchi of lungs dilate and increase gas exchange, adrenaline raises blood glucose levels

Parasympathetic: opposes sympathetic system, calms body, decreases heart/breathing rate, enhances digestion

Neurons Sensory Neuron: detects a stimulus at one or

more receptor endings and relays information about it to other neurons

Motor Neuron: delivers excitatory or inhibitory commands from other neurons to muscles or glands

Interneurons: information from most sensory neurons flows through these before it gets to motor neurons

Receive, process, and store sensory information

The Neuron Basic functional unit of the nervous system Cell body: contains nucleus and other

organelles Dendrites: sensory; receive incoming

messages from other cells and carry electrical signals to the cell body

Axons: transmit an impulse from the cell body outward to another cell Has only one axon, most wrapped in myelin sheet that protects it and speeds the impulse

Membrane Gradients and Potentials Membrane potential: difference in electrical

charge between the cytoplasm (negative charge) and extracellular fluid (positive)

Membrane Gradients and Potentials Resting Membrane Potential: the steady

voltage difference across the neuron’s plasma membrane Is about -70 millivolts Negative sign indicates that the inside of the cell

is negative relative to the outside of the cell

Membrane Gradients and Potentials Action Potential:

an impulse generated in the axon of a neuron

When stimulated to overcome threshold permeability of a region of the membrane changes

Sodium-Potassium Pump When neuron at rest

About 15 sodium ions in the fluid inside of plasma membrane for every 150 outside

About 150 potassium ions inside for every 5 outside

Creates ion gradients

Sodium-Potassium Pump Threshold overcome by axon stimulation Sodium channels open and sodium floods into

the cell, down concentration gradient Potassium channels open and potassium

floods out of the cell Wave of depolarization: rapid movement of

ions, reverses polarity of membrane (action potential)

Sodium-Potassium Pump Pump restores membrane to original state by

pumping sodium and potassium ions back to original positions Repolarization Refractory period: neuron cannot respond to

another stimuli (ensures impulse moves along axon in only one direction)

Sodium-Potassium Pump Action potential is like dominos

First action potential generates a second which generates a third

Impulse moves along axon, without losing strength, if axon myelinated can travel faster

Sodium-Potassium Pump Action potential is all-or-non event

Either stimulus is strong enough or isn’t Strong stimulus sets up more action potential than

a weak one does

The Synapse Thin cleft separates output zone of one

neuron from a neighboring neuron, gland cell, or muscle cell

At this zone, electrochemical energy of action potential is transduced to the form of chemical signal that can diffuse across the cleft and activate or inhibit target cell

Chemical synapse: functional bridge between a neuron and some other cell

Synapse means to fasten together

The Synapse Neurotransmitter: type of signaling

molecule that is synthesized in neurons only Plasma membrane has many gated channels

for calcium ions In between action potentials, more calcium

ions outside than inside (gate are shut)

The Synapse Action potential makes gates open- calcium

ions flow in, synaptic vesicles move through cytoplasm in the axon ending and fuse with the membrane

Release neurotransmitter by exocytosis into the synapse, which sets up another potential on adjacent cell

Shortly after neurotransmitter released, is destroyed by an enzyme which stops the impulse at that point

The Synapse Most common neurotransmitters:

Acetylcholine: can be inhibitory or excitatory Serotonin Epinephrine Norepinephrine Dopamine GABA

Synaptic Integration Excitatory Postsynaptic Potential (EPSP):

is the electrical charge caused by the binding of the neurotransmitter to its receptor on the postsynaptic membrane Has depolarization effect, drive membrane closer

to threshold Inhibitory Postsynaptic Potential (IPSP):

is the voltage charge associated with chemical signaling at an inhibitory synapse Hyperpolarizing effect, can help drive membrane

farther from threshold or help maintain it at resting level

Synaptic Integration Synaptic Integration: postsynaptic neuron

sums all signals that are arriving at its input zone on more than one communication line Two or more incoming signals may be dampened,

suppressed, reinforced, or sent on to other cells

Types of NeurotransmittersNeurotransmitter

Functions

Acetylcholine In skeletal muscles can stimulate contraction; in heart muscles it slows contraction.

Norepinephrine, epinephrine (adrenaline), dopamine

Made from tyrosine (A.A), prime body to respond to stress. Dopamine affects fine motor control and pleasure seeking behaviors (destruction of them causes Parkinson’s).

Serotonin Derived from tryptophan (A.A), affects mood and memory, low levels associated with depression.

GABA (gamma amino butyric acid)

Derived from glutamate (A.A), in the brain it is the major inhibitor of neurotransmitter release by other neurons.

Neuropeptides Neuropeptides: larger than neurotransmitters

Act as neuromodulators: magnify or reduce the effects of neurotransmitter on neurons that are either close to the secreting cell or some distance away

Examples: Substance P: enhances pain perception Enkephalins and endorphins: natural painkillers

and resemble morphine in their structure, inhibit substance P, secreted in response to strenuous activity or injuries, can elevate mood and enhance function of immune cells

Endorphins released when people laugh, acupuncture, massage

The Reflex Arc Simplest nerve response Inborn, automatic, and protective Ex. Knee jerk reflex

Consists of only a sensory and a motor neuron Impulse moves from sensory neuron in your knee to the motor neuron that directs the thigh muscle to contract Spinal cord not involved

The Reflex Arc More complex reflex arc: 3 neurons-

a sensory, a motor, and an interneuron or association neuron

Sensory neuron transmits an impulse to the interneuron in the spinal cord which sends one impulse to the brain for processing and also one to the motor neuron to effect change immediately (at the muscle)

This is the response that quickly jerks your hand away from a hot iron before your brain has figured out what has occurred

The Vertebrate Brain Brain is divided into

specialized regions: forebrain, midbrain, hindbrain

Brain stem: most ancient nervous tissue, persists in all three regions and is continuous with spinal cord

Forebrain

Hindbrain

Midbrain

The Vertebrate Brain Hindbrain:

Medulla oblongata: houses reflex centers for respiration, circulation, and other essential tasks , governs some reflexes (coughing), affects sleep

Cerebellum: uses inputs from eyes, ears, muscle spindles, and forebrain regions to help control motor skills and posture Axons from its two halves reach the pons (bridge),

control signal flow between the cerebellum and integrating centers in forebrain

The Vertebrate Brain Midbrain:

Has centers for visual input Forebrain has took over task integrating most

visual stimuli

The Vertebrate Brain Forebrain:

Cerebrum: two cerebral hemispheres Thalamus: sorting out sensory input and relaying

it to the cerebrum Hypothalamus: main center for homeostatic

control of the internal environment; assesses and regulates all behaviors related to internal organ activities, such as thirst, sex, and hunger; governs related emotions, such as sweating with passion and vomiting with fear

The Vertebrate Brain Cerebrospinal fluid: forms inside brain

ventricles, seeps out and bathes tissues of brain and spinal cord; cushions them against potentially jarring movements

Blood-brain barrier: protects spinal cord and brain from harmful substances Exerts some control over which solutes enter

cerebrospinal fluid

The Human Cerebrum Each half of cerebrum (cerebral hemisphere)

is divided into 4 lobes Frontal, temporal, occipital, parietal

The Human Cerebrum Cerebral Cortex: grey matter at

surface of each lobe, distinct areas receive and process different signals, still interact

Two hemispheres overlap in function Left more concerned with analytical skills, math,

speech Right interprets music, judges spatial relations,

assesses visual inputs

Grey Matter: areas of neuron cell bodies, dendrites, and unmyelinated axons, plus neoroglia, in brain and spinal cord

White Matter: consists mostly of myelinated axons

The Human Cerebrum Motor Areas:

Body is spatially mapped out in primary motor cortex of each frontal lobe- controls and coordinates the movements of skeletal muscles on opposite side of the body

Premotor cortex of each frontal lobe governs leaned patterns of motor skills Ex. Dribble a basketball

Broca’s area helps translate thoughts into speech

The Human Cerebrum Sensory Areas:

Primary somatosensory cortex is located at front of parietal lobe

Organized as a map corresponding to body’s parts Receiving center for sensory input from skin and

joints Taste perception At back of occipital lobe, primary visual cortex receives signals from eyes Temporal lobe: perceptions of sound and odor

The Human Cerebrum Association Areas:

Scattered through cortex, not in primary motor and sensory areas

Ex. Visual association area around primary visual cortex compares what we see with visual memories

Prefrontal cortex: foundation of our personality and intellect, of abstract thought, judgment, planning, and concern for others

Limbic System Limbic System: encircles upper brain stem Governs emotions, assists in memory,

correlates organ activities with self-gratifying behavior

Includes hypothalamus, part of thalamus, and cingulate gyrus, hippocampus, and amygdala

Reticular Formation Reticular Formation: low level path to

motor centers in medulla oblongata and spinal cord Network of interneurons, extends from upper

spinal cord, through brain stem, and into cerebral cortex

Promotes chemical changes that affect states of consciousness, such as sleeping or waking