The Neuron
- neurons--the nerve cells that transfer information within the body
- the body uses them to send long-distance pulses of electric current to send out, receive, and regulate the flow of information
- more high functioning, complex animals need groups of neurons organized into a brain or simpler clusters called ganglia to function
- neurons have very specific and highly specialized cellular organizations, including the cell body, axon, dendrites, myelin sheath, and synapses
- cell body--where the neuron's organelles (including nucleus) are located
- dendrites--branched extensions on a neuron that receive signals from other neurons
- axon--every neuron has a single axon, which transmits the signal to other neurons
- Shwann cells-- form a myelin sheath, a layer of electrically insulating tissue, around its axon; protects the axon as well as allows impulses to transmit quickly and efficiently from nerve cell to nerve cell
- synapse--a junction between cells that the signal is passed through
Action Potential
- hyperpolarization--the increase in magnitude of the membrane potential; makes the inside of the membrane more negative
- depolarization--the decrease in the magnitude of the membrane potential
- shift in membrane potential is called a graded potential
- if depolarization shifts the membrane potential sufficiently the result is a massive charge in membrane voltage, called action potential
- action potential spread along the axons of a neuron makes them well suited for transmitting long-distance electrical signals through the body
- neurons contain gated ion channels that open or closes in response to a certain stimuli; the opening/closing changes the membrane's permeability to certain ions, which then alters membrane potential
- when gated potassium channels are stimulated to open, there is an increase in the membrane's permeability to K+; therefore, net diffusion of K+ out of the neuron increases, shifting the membrane potential toward EK (-90 mV at 37 degrees C)
Information Passing from Neuron to Neuron
Dopamine, made from tyrosine, is a neurotransmitter that, when being released properly, is released at many different sites in the brain. It affects sleep, mood, attention and learning. Psychoactive drugs including LSD produce their hallucinatory effects by binding to brain receptors for these neurotransmitters. Dopamine is associated with different disorders and diseases as well; a lack of dopamine in the brain can cause Parkinson's disease. Depression is usually treated with different drugs that increase levels of dopamine and serotonin, another neurotransmitter, in the brain.
Regions of the Human Brain
- cerebellum--coordinates movement and balance and helps in learning motor skills as well;aids in receiving input from the auditory and visual systems
- amygdala-- is a brain structure that deals with the most important role in storage of emotional memory located near the base of the cerebrum where autonomic arousal is measured by increased heart rate and sweating
- neurohormones--molecules that are secreted by a neuron that travels in body fluids and acts in specific target cells, changing their functioning; example would be vasopressin, a hormone essential to kidney function and water balance
- brainstem-- consists of midbrain (pods and medulla) and integrates several types of sensory information and sends it to specific regions of the forebrain; major function o fthe pons and medulla is to transfer information between the peripheral nervous system and the mid/forebrain and also aid in body movements; midbrain coordinates visual reflexes such as the peripheral vision reflex
- hindbrain-- is associated with visual asssociation by combing images and object recognition
- occipatal lobe-- is located in the hind brain as well as the cerebellum; it is the visual cortex, processing visual stimuli and pattern recognition
- temporal lobe--located beneath the frontal lobes on the sides of the head; auditory cortex, involved in hearing; contains Wernicke's arae, which is in control of language comprehension
- parietal lobe--located on the top of the head towards the back; involved in sensory association and integration of sensory information; includes the somatosensory cortex which controls sense of touch
- frontal lobe--located at the front of the head; contains the motor cortex, which controls skeletal muscles, the prefrontal cortex, which is involved in decision making and planning, and Broca's area, which controls speech formation