integrative function of the nervous system. lecture overview overview of the brain neurotransmitters...

Integrative Function of the Nervous System

Lecture Overview

• Overview of the Brain• Neurotransmitters• The Brain

The Nervous System

Central Nervous System

• The CNS is composed of the brain and spinal cord

• Spinal cord connects the brain with the PNS– Spinal cord is comprised of cell bodies and

axons that carry messages• Afferent: toward the brain (sensory function)• Efferent: away from the brain (motor function)

Peripheral Nervous System

• The Peripheral Nervous System (PNS) includes all nerves outside the brain and spinal cord– Somatic NS carries sensory messages to

brain and motor commands to the muscles– Autonomic NS regulates automatic body

functions (such as heart rate, breathing)• Sympathetic: “Fight or Flight”• Parasympathetic: dominant when relaxed

The Autonomic Nervous System

The Spinal Cord

Myelin

• Myelin is a fatty, waxy substance coating the axon of some neurons.

• Functions:– Speeds neurotransmission– Insulates neurons from each other– Makes neurotransmission more efficient

Synapse• The synapse is the junction between an

axon terminal and an adjacent dendrite or cell body.

• Neurotransmitter (NT) molecules are released from the axon terminal into the synapse when the action potential arrives at the axon terminal.

The Synapse

1. Synthesis of neurotransmitter (NT)

2. Storage and transport of NT within vesicles

3. NT Release4. Activation of

postsynaptic receptors5. Termination of

transmitter effect (e.g. reuptake)

Neurotransmitters

• Serotonin • Acetylcholine• Dopamine• Norepinephrine• Epinephrine• GABA• Endorphins

Psychoactive Drugs• Psychoactive drugs affect the

nervous system to alter mood, emotion, and thought

• Psychoactive drugs act by:– Increasing or decreasing release

of neurotransmitters – Stimulating or blocking receptor

sites

Psychoactive Drugs

• Agonists enhance neurotransmitter function

• Antagonists block neurotransmitter function

Midline Brain View

Brainstem

• Brainstem is a primitive portion of brain– Pons: involved in respiration, sleep regulation,

dreaming– Medulla: involved in life support functions such as

respiration and heart rate– Reticular activating system is an arousal system

within the brainstem

Subcortical Brain Areas

• Corpus callosum: band of axons that interconnects the hemispheres

• Thalamus: sensory relay area

• Limbic system: involved in emotionality

• Hypothalamus: feeding, fleeing, mating, fighting, homeostasis

• Cerebellum: involved in motor control

HYPOTHALAMIC REGULATION OF PHYSIOLOGIC FUNCTIONS

•Water and electrolyte balance

•Temperature regulation

•Activation of sympathetic nervous system

•Thirst and regulation of drinking

•Hunger, satiety and regulation of feeding

•Regulation of sexual behavior

•Regulation of circadian rhythms

•Pituitary hormone secretion

HYPOTHALAMUS CONTAINS “BIOLOGIC CLOCK”

•Hypothalamus plays a major role in regulating biologic rhythms

•Rhythms persist in absence of time cues

•Circadian or diurnal rhythms repeat daily

•External signals of light and darkness serve to entrain the internal clock to a 24 hour day

•Biologic clock is located in the suprachiasmatic nucleus

•Input is received from the eye by the retinohypothalamic tract of the optic nerve

Limbic SystemThe fornix is a C-shaped bundle of fibres (axons) in the brain, and carries signals from the hippocampus to the mammillary bodies and septal nuclei.

The amygdala is an almond-shaped group of nuclei located deep within the medial temporal lobes of the brain in complex vertebrates, including humans. Primary role in the processing and memory of emotional reactions and considered part of the limbic system.

The hippocampus plays important roles in long-term memory and spatial navigation. Like the cerebral cortex, with which it is closely associated, it is a paired structure, with mirror-image halves in the left and right sides of the brain.

LIMBIC SYSTEM FUNCTIONS

BRAIN REWARD SYSTEMS

•Electrical stimulation of various sites in the limbic system produces either pleasurable (rewarding) or unpleasant (aversive) feelings

•Dopaminergic neurons play a major role in mediating reward

AGGRESSION

•Stimulation of sites in hypothalamus and amygdala elicits a fight or flight reaction and postures of rage and aggression

•Severing the cortical connections to the limbic system results in permanent rage postures and aggressiveness

SEXUAL ACTIVITY

•Limbic system in general coordinates sex drive and mating behavior

•Higher cortical centers exert more or less overriding influences

MEMORY AND LEARNING

Most likely sites are large association areas of the cerebral cortex working in association with subcortical structures as hippocampus and amygdalaPrefrontal cortex is important for coordinating formation of memoryHippocampus is important in consolidating memoryAssociation cortices are important in storing memories

Short term memoryProduct of working memory-prefrontal cortex

Long term memoryInvolves limbic system input

Cerebral Cortex• Cortex refers to the outer covering of the brain

– Consists of left and right hemispheres

– Cortex is divided into lobes• Frontal: Self-awareness, planning, voluntary movement,

emotional control, speech, working memory• Parietal: Body sensations• Occipital: Vision• Temporal: Hearing, language comprehension

Cortical Lobes

Summary of Hemispheric Specializations

Motor and Somatosensory Cortex

Split-Brain Research

• When a split-brain patient is asked to stare straight ahead while a photo of a fork is flashed to his left visual field, he cannot name it.

Split-Brain Research