Nervous System

Nervous SystemNervous System

AP Biology

Ch. 48

Ms. Haut

Function of Nervous SystemFunction of Nervous System

Sensory Input– Conduction of signals from sensory receptors

Integration– Carried out by Central Nervous System (CNS)

Brain and spinal cord

Motor Output– Carried out by Peripheral Nervous System (PNS)– Conduction of signals to muscle or gland cells– Carry out body’s responses to stimuli

Animal Nerve Cells Animal Nerve Cells Nerves: rope-like bundles of extensions of

neurons, tightly wrapped in connective tissue

Neurons: functional unit of the nervous system

Functional Organization of Functional Organization of NeuronsNeurons

Sensory Neurons: relay information (stimuli) from the external and internal environments to CNS

Interneurons: integrate sensory input and motor output (carry stimuli in the brain and spinal cord)

Motor Neurons: convey impulses from CNS to effector cells in muscles or glands

Glial cells: support, protect, and nourish neurons

Structural Diversity of NeuronsStructural Diversity of Neurons

Overview of Vertebrate Nervous SystemOverview of Vertebrate Nervous System

Neuron CircuitryNeuron Circuitry

Simplest neural circuit involves synapses between 2 neurons, a sensory neuron and a motor neuron

Result is often an automatic response called a reflex

The Knee-jerk ReflexThe Knee-jerk Reflex

http://bio.rutgers.edu/~gb102/lab_5/103ar.html

Neural SignalsNeural Signals

Nerve impulse is an electrical signal that depends on the flow of ions across the plasma membrane of a neuron

Membrane Resting PotentialMembrane Resting Potential

Cell is said to be polarized

Action PotentialAction Potential

A nerve impulse is generated when the difference in electrical charge disappears

Occurs when a stimulus contacts the tip of a dendrite and increases the permeability of the cell membrane to Na+ ions

Cell is said to be depolarized

Graded PotentialsGraded Potentials

“All-or-none event”

Regulation of Action PotentialRegulation of Action Potential

Propagation Propagation of the Action of the Action

PotentialPotential After the wave

of depolarization has passed, the neuron reestablishes the difference in charges by pumping K+ out of the cytoplasm

Saltatory ConductionSaltatory Conduction

SynapsesSynapses

Nerve impulses pass down the dendrite, through the cell body, and down the axon.

At the end of the axon, the signal reaches a fluid-filled space (synapse) separating the end of the axon from the dendrite of the next neuron.

Neuromuscular junction: synapse located at the junction of a neuron and muscle fiber

Chemical SynapseChemical Synapse

MAJOR NEUROTRANSMITTERS AND THEIR EFFECTS

Acetylcholine (ACh)

Generally excitatory

Affects arousal, attention, memory, motivation, movement. Too much: spasms, tremors. Too little: paralysis, torpor.

Dopamine Inhibitory Inhibits wide range of behavior and emotions, including pleasure. Implicated in schizophrenia and Parkinson's disease.

Serotonin Inhibitory Inhibits virtually all activities. Important for sleep onset, mood, eating behavior.

Norepinephrine Generally excitatory

Affects arousal, wakefulness, learning, memory, mood.

Endorphins Inhibitory Inhibit transmission of pain messages.

Organizations of InvertebratesOrganizations of InvertebratesWithout CNS

CN

S

CN

S

(PNS)

Vertebrate Vertebrate Nervous Nervous SystemSystem

Autonomic Nervous SystemAutonomic Nervous System

Works on an involuntary basis2 subdivisions

Parasympathetic Sympathetic

Return body to normal after an emergency

Prepare body for emergency

Heart rate slows, pupils constrict, blood vessels dilate

Increase heart rate, constricted blood vessels, pupils dilate

Roles of Roles of Parasympathetic Parasympathetic and Sympathetic and Sympathetic Divisions of the Divisions of the Autonomic Autonomic Nervous SystemNervous System

Structure of BrainStructure of Brain

BrainstemBrainstem Medulla oblongata

– Contains centers that control visceral (autonomic, homeostatic) functions

Breathing, heart and blood vessel activity, swallowing, vomiting, and digestion

Pons – Have nuclei in the medulla that regulate breathing centers

Midbrain– Centers for receipt and integration of sensory information

Coordinates large-scale body movements such as walking

CerebellumCerebellum

Primary function is coordination of movement

Receives information about position from joints and length of muscles, as well as auditory and visual systems

Plays role in learning and remembering motor responses (hand-eye coordination)

Thalamus and Thalamus and HypothalamusHypothalamus Thalamus

– Main input center for sensory information going to cerebrum– Receives input from cerebrum to regulate emotion and

arousal Hypothalamus

– Source of posterior pituitary hormones and releasing hormones that act on anterior pituitary

– Regulates body temp, thirst, hunger, other basic survival mechanisms

– Plays role in sexual response and mating behaviors, fight-or-flight response, and pleasure

Structure and Function of Structure and Function of CerebrumCerebrum

Sleep and ArousalSleep and Arousal

Controlled by several centers in the cerebrum and brainstem

Reticular formation: neurons that pass through the brainstem– Reticular activating system--regulates sleep and arousal– Increased input to cortex, increases alertness

Medulla and pons– Nuclei stimulated induces sleep– Serotonin may activate sleep centers

Lateralization, Language, and Lateralization, Language, and SpeechSpeech

Association areas of cerebral cortex are lateralized (specialized functions)

Left hemisphere– Speech, language, calculation, and rapid serial

processing of details

Right hemisphere– Overall context, spatial perception, and creative

abilities

EmotionsEmotions

Limbic system-functional group of nuclei and interconnecting axon tracts in the CNS– Includes parts of the thalamus and hypothalamus, and

portions of the cerebral cortex– Linked to areas of cerebral cortex involved with

complex learning, reasoning, and personality

Amygdala-prominent component of limbic system– Major organizer of emotional information– Plays role in memory association