Starting small: The Neuron
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Transcript of Starting small: The Neuron
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
malfunctionsAcetylcholine
(ACh)Enables muscle action,
learning & memoryAlzheimer’s disease less ACh production
Dopamine Influences movement, learning, attention, &
emotion
Excess schizophreniaUndersupply
Parkinson’s diseaseSerotonin Affects mood, hunger,
sleep, and arousalUndersupply
depressionNorepinephrine Helps control alertness &
arousalUndersupply
depressed moodGlutamate Excitatory neurotransmitter
involved in memoryExcess
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.