Starting small: The Neuron

• neuron: a nerve cell; receives signals from other neurons or sensory organs, processes these signals, and sends signals to other neurons, muscles, or bodily organs– the basic unit of the nervous

system

The Neuron• 3 types of neurons:

– 1. sensory neurons: respond to input from sensory organs (skin, eyes, etc.)

– 2. motor neurons: send signals to muscles to control movement

– 3. interneurons: connect the sensory neurons and motor neurons

• most of the neurons in the brain = interneurons

• average human brain 100 billion neurons

Structure of the Neuron

Structure of the Neuron

• cell body (soma): the central part of the neuron, contains the nucleus– regulates cell functioning

• dendrites: the branching part of the neuron that receives messages from other neurons and relays them to the cell body

Structure of the Neuron

• axon: the long, cable-like extension that delivers messages to other neurons

• myelin sheath: layer of fatty tissue that insulates the axon and helps speed up message transmission– multiple sclerosis: deterioration of myelin leads to slowed communication

with muscles and impaired sensation in limbs• knobs: structure at the end of one of the axon’s branches that

releases chemicals into the space between neurons, when the neuron is fired

From Neuron to Neuron

• ≈100 billion neurons in a human brain, connected to an average of 10,000 others; some up to 100,000

• synapse: the place where an axon of one neuron meets with the dendrite/cell body of another neuron

From Neuron to Neuron

From Neuron to Neuron

• neurotransmitters: a chemical that sends signals from one neuron to another over the synapse

From Neuron to Neuron• Neurotransmitters are

stored in vesicles in the knobs, and bind to receptors on the cell membrane of the next neuron.– Each receptor can

only bind with one kind of neurotransmitter.

(Some) NeurotransmittersNeurotransmitter Function Examples of

malfunctions

Acetylcholine (ACh)

Enables muscle action, learning & memory

Alzheimer’s disease less ACh production

Dopamine Influences movement, learning, attention, &

emotion

Excess schizophreniaUndersupply

Parkinson’s disease

Serotonin Affects mood, hunger, sleep, and arousal

Undersupply depression

Norepinephrine Helps control alertness & arousal

Undersupply depressed mood

Glutamate Excitatory neurotransmitter involved in memory

Excess overstimulation of

brain, seizures

The Nervous System

• comprised of the central nervous system and the peripheral nervous system

• central nervous system: brain and spinal cord– reflex: an automatic response to an event

• e.g. sensory neuron detects pain, send signal to spinal cord signal to interneurons signal to motor neurons

The Nervous System

• Peripheral Nervous System: links central nervous system to organs–comprised of the skeletal nervous

system and the autonomic nervous system

–skeletal nervous system: controls voluntary movements of our skeletal muscles

The Nervous System

• autonomic nervous system: controls many of the self-regulatory functions of the body (e.g. digestion, circulation)– comprised of the sympathetic and parasympathetic

nervous systems– sympathetic: prepares us for defensive actions against

threats (e.g. faster heartrate, increased breathing rate, inhibits digestion, dilates pupils to allow greater light sensitivity)

– parasympathetic: counteracts effects of sympathetic nervous system, calms us down

Structure of the Brain

• The human brain is comprised of “older” and “newer” parts.– “older”: lower level

structures, responsible for basic survival mechanisms

– “newer”: higher level structures, responsible for more advanced human faculties

Structure of the Brain

• brainstem: the set of neural structures at the base of the brain, including the medulla, the reticular formation, and the pons– facilitates communication

between the brain and spinal cord

The Brainstem• medulla: controls

heartbeat, breathing, and swallowing

• pons: bridge from brainstem to cerebellum; controls a variety of functions, including sleep and control of facial muscles

The Cerebellum• “little brain” extending

from rear of brainstem– coordinates physical

movement– contributes to

estimating time and paying attention

• cerebellum + other lower level brain structures occur without conscious effort– Much of our brain’s

activity occurs outside of our awareness

The Brainstem• thalamus: the brain’s

sensory switchboard; receives signals from the sensory and motor systems, and relays them to the appropriate parts of the brain – also receives signals from

higher brain structures, relays them to medulla and cerebellum

The Limbic System

• limbic system: doughnut-shaped system of neural structures at the border of the brainstem and cerebral hemispheres– involved in the basics of

emotion and motivation: fighting, fleeing, feeding, and sex

– comprised primarily of the hypothalamus, the hippocampus, and the amygdala

The Limbic System• hypothalamus: brain

structure that sits under the thalamus and plays a central role in controlling eating and drinking, and in regulating the body’s temperature, blood pressure, and heart rate

The Limbic System• hippocampus: brain

structure that plays a key role in allowing new information to be stored in memoryhippocampus does not

contain memories itself, but does trigger processes that store memories elsewhere in the brain

The Visible Brain• cerebral cortex: the

convoluted pinkish-gray surface of the brain, where most mental processes take place

• The brain is divided into two halves (cerebral hemispheres), separated by a deep fissure– hemispheres control

opposite side of body (e.g. right-handers’ writing is controlled by the left hemisphere)

Our Divided Brains

• cerebral hemispheres connected by the corpus callosum, a large band of neural fibers that transmits messages between hemispheres– contains more than 200

million nerve fibers, can transfer more than 1 billion bits of information per second

Structure of the Cortex• cerebral cortex divided

into lobes, or regions of the brain– Each lobe is

(roughly) responsible for different higher-level functions, but remember that they do not work merely in isolation.

Structure of the Cortex

• occipital lobe: brain lobe at the back of the head– responsible primarily

for vision; separate areas specify visual properties such as shape, color, and motion

Structure of the Cortex• temporal lobe: the brain

lobe under the temples, in front of the ears– many functions,

including processing sounds, committing information to memory, and comprehending language

Structure of the Cortex

• parietal lobe: brain lobe at the top and center/rear of the head– involved in registering

spatial location, attention, and motor control

Structure of the Cortex• frontal lobe: the brain lobe

located behind the forehead– the seat of planning,

memory search, motor control, reasoning, emotions, and many other functions

– In many ways, the frontal lobe is what makes us uniquely human.