C3: Biological Bases of Behaviour

Dendrites

Dendrites

Rootlike parts of the cell that stretch out from the cell body. Dendrites grow to make synaptic connections with other neurons.

Cell Body (Soma)

Contains the nucleus and other parts of the cell needed to sustain its life.

Axon

Wirelike structure ending in the terminal buttons that extends from the cell body.

Myelin Sheath

A fatty covering around the axon of some neurons that speeds neural impulses

Terminal Buttons

The branched end of the axon that contains neurotransmitters

Neurotransmitters

Chemicals contained in the terminal buttons that enable neurons to communicate. They fit into receptor sites on the dendrites of neurons like a key in a lock.

Synapse

The space between the terminal buttons of one neuron and the dendrites of the next neuron.

How does a neuron “fire”?

In the resting state, a neuron has a negative charge (negative ions in the cell and positive ions surrounding it). The cell membrane is selectively permeable to prevent them from mixing.

Reaction begins when terminal buttons of neuron A are stimulated and release neurotransmitters into the synapse. These neurotransmitters fit into receptor sites of neuron B.

If enough neurotransmitters are received (threshold), the membrane of neuron B becomes permeable and positive ions rush through the cell (action potential). When the charge reaches the terminal buttons of neuron B, the buttons release their neurotransmitters into the synapse.

The process may begin again if enough neurotransmitters are received by that next cell to pass the threshold.

All-or-none Principle

A neuron either fires completely or it does not fire. If the dendrites of a neuron receive enough neurotransmitters to push the neuron past its threshold, the neuron will fire completely.

Acetylcholine

Motor movement; lack → Alzheimer’s disease

Dopamine

Motor movement + alertness; lack → Parkinson’s disease, excess → Schizophrenia

Endorphins

Pain control; involved in addictions

Serotonin

Mood control; lack → clinical depression

GABA

Inhibitory neurotransmitter; lack/excess → seizures, sleep problems

Glutamate

Excitatory neurotransmitter, involved in memory; lack/excess → migraine, seizures

Norepinephrine

Alertness, arousal; excess/deficit → depression

Afferent Neurons

Sensory neurons; Take info from the senses to the brain

Interneurons

Once info reaches the brain/spinal cord, interneurons take the messages and send them elsewhere in the brain or onto efferent neurons.

Efferent Neurons

Motor neurons; Take info from the brain to the rest of the body

Central Nervous System

All nerves encased within bone (brain + spinal cord)

Peripheral Nervous System

All nerves NOT encased within bone (contains somatic and autonomic nervous system)

Somatic Nervous System

Controls our voluntary muscle movements (using impulses from the motor cortex)

Autonomic Nervous System

Controls the automatic functions of our body and responses to stress. (contains the sympathetic and parasympathetic nervous systems)

Sympathetic Nervous System

Mobilizes our body to respond to stress. It accelerates some functions (e.g. heart rate, blood pressure, respiration), but conserves resources needed for a quick response by slowing down other functions (e.g. digestion).

Parasympathetic Nervous System

Causes our body to slow down after a stress response.

Reflexes

Reactions that occur the moment sensory impulses reach the spinal cord

Accidents

By observing the brain damage and behaviour after an accident, researchers can determine the functions the damaged part played in behaviour.

Lesions

• The removal or destruction of part of the brain

• Observe behaviour afterwards to determine function of that part of the brain

• Frontal Lobotomy (In the past, lesioning of frontal lobe was used to make the patients calm and relieve symptoms)

Electroencephalogram (EEG)

• Detects brain waves

• Examine what type of waves the brain produces during different stages of consciousness and use this information to generalize about brain function.

Computerized Axial Tomography Scan (CT)

• Several X-ray cameras that rotate around the brain and combine all the pictures into a detailed 3D picture

• Only show structure, not the functions or activity

Magnetic Resonance Imaging (MRI)

• Uses magnetic fields to measure the density and location of brain material.

• Only show structure, not functions or activity

Positron Emission Tomography Scan (PET)

• Shows what areas of the brain are most active during certain tasks

• Measures how much of a certain chemical parts of the brain are using

Functional MRI (fMRI)

• Combines elements of MRI and PET scans

• Show details of brain structures with information about blood flow in the brain

Hindbrain

Life support system; controls the basic biological functions that keep us alive (contains medulla, pons, cerebellum)

Medulla

Control of blood pressure, heart rate, and breathing

Pons

Control of facial expression

Cerebellum

Controls habitual muscle movements

Midbrain

Coordinates simple movements with sensory information

Reticular Formation

Netlike collection of cells throughout the midbrain that controls general body arousal and ability to focus our attention.

Forebrain

Controls thought and reason (contains thalamus, hypothalamus, amygdala, hippocampus)

Thalamus

Receives the sensory signals coming up the signal cord and sends them into the appropriate areas in the rest of the forebrain.

Hypothalamus

Controls several metabolic functions (e.g. body temperature, sexual arousal, hunger, thirst, and the endocrine system)

Amygdala

Vital to experiences of emotion

Hippocampus

Vital to our memory system (memories are processed through this area and then sent to other locations in the cerebral cortex for permanent storage).

Cerebral Cortex

• Grey wrinkled surface of the brain (layer of densely packed neurons)

• Overtime, the dendrites of the neurons grow and connect with other neurons to form the complex neural web

Fissures

Wrinkled surface of the cerebral cortex to increase surface area

Contralateral control

Left hemisphere controls sensory and motor functions of the RIGHT half of the body whereas the right hemisphere controls sensory and motor functions of the LEFT half of the body.

Brain Lateralization

Specialization of function in each hemisphere

• Research is done by examining split-brain patients

• Corpus callusum (nerve bundle that connects the two hemispheres) is cut to treat severe epilepsy

• Operation pioneered by Roger Sperry and Michael Gazzaniga

• Cannot orally report info only in the right hemisphere since spoken language is in the left hemisphere

Association areas

Any area of the cerebral cortex that is not associated with receiving sensory info or controlling muscle movements.

Frontal lobes

Large areas of the cerebral cortex located at the top front part of the brain behind the eyes.

Prefrontal cortex

Anterior/front of the frontal lobe is the prefrontal cortex and is thought to play a critical role in directing thought processes.

Motor cortex

A thin vertical strip at the back of the frontal lobe that sends signals to our muscles, controlling our voluntary movements. The top of the body is controlled by neurons at the bottom of this cortex, progressing down the body as you go up the cortex.

Parietal Lobes

Located behind the frontal lobe but still on the top of the brain

Sensory cortex

A thin vertical strip in the parietal lobe that receives incoming touch sensations from the rest of our body. It’s organized similarly to the motor cortex - the top of the sensory cortex receives sensations from the bottom of the body and the bottom receives sensations from the top of the body.

Occipital Lobes

Interpret messages from our eyes in our visual cortex

• Impulses from right half of each retina are processed in the visual cortex in the right occipital lobe

• Impulses from left half of each retina are processed in the visual cortex in the left occipital lobe

Temporal Lobes

Process sound sensed by our ears

• Sound received by either ear is processed in both auditory corticies

Broca’s area

Frontal lobe; responsible for controlling muscles involved in producing speech

Wernicke’s area

Temporal lobe; interprets both written and spoken speech

Brain Plasticity

The ability of the nervous system to change its activity in response to intrinsic or extrinsic stimuli by reorganizing its structure, functions, or connections.

Endocrine System

• A system of glands that secrete hormones that affect many different biological processes in our bodies

• Controlled by hypothalamus

Adrenal Glands

• Produce adrenaline

• Signals body to prepare for fight or flight (autonomic nervous system - involuntary responses)

Thomas Bouchard

Studied twins raised in different families to see if traits were nurture or nature (criticized because twins share the same physical characteristics, causing others to treat them in similar ways)