Nervous System Anatomy

• The central nervous system (CNS) comprises the brain and spinal cord.
• The CNS receives and transmits neural messages to the peripheral nervous system (PNS).

Functions of the Brain

• Regulates and coordinates mental processes, behavior, and bodily activity.
• Enables higher-order thinking.

Spinal Cord

• A cable of nerve tissue extending from the brain.
• Transmits sensory (afferent) and motor (efferent) messages.

Peripheral Nervous System (PNS)

• Includes all neurons outside the CNS.
• Divided into the somatic and autonomic nervous systems.
• Transmits neural messages between the CNS and the body.

Autonomic Nervous System

• Regulates visceral muscles, organs, and glands.
• Transmits neural messages to the CNS about their activity.

Sympathetic Nervous System

• Activates visceral muscles, organs, and glands.
• Prepares the body to respond to a threat or stressor.

Parasympathetic Nervous System

• Maintains optimal functioning of visceral muscles, organs, and glands.
• Maintains homeostasis and returns the body to optimal functioning after arousal.

Somatic Nervous System

• Transmits neural messages related to voluntary motor movement.
• A network of neurons that transmits sensory information to the CNS.
• Carries motor information to skeletal muscles to initiate movement.

Sympathetic Nervous System and Fight-Flight Response

• Initiates the fight-flight response.

Freeze Response

• Brief period activated by the parasympathetic nervous system.
• Bodily reactions, like blood pressure, drop below normal levels.
• The body lacks adequate energy levels for fight or flight.

Neuron

• A nerve cell that transmits neural information.

Sensory Neurons

• Carry sensory information to the CNS through afferent pathways.

Motor Neurons

• Carry commands from the CNS to muscles.

Interneurons

• Connect sensory and motor neurons within the CNS.

Typical Neural Communication

• Sensory neuron receptors detect stimuli.
• The CNS processes information.
• Motor neurons carry the response to muscles.

Spinal Reflex

• Unconscious response to sensory stimuli.
• Initiated by interneurons in the spinal cord, independent of the brain.

Unconscious Response

• Automatic and involuntary action performed without conscious awareness.
• Responds to internal and external sensory stimuli.
• Physiological responses of the autonomic nervous system are an example.
• The spinal reflex is also an example of this type of response.

Conscious Response

• Deliberate and voluntary action initiated by the brain.
• Performed intentionally by the body.

Dendrites

• Receive messages from other neurons.

Soma

• Maintains the neuron and processes information.

Axon

• Transmits electrical impulses away from the soma.

Myelin

• Insulates the axon to speed up neural transmission.

Axon Terminals

• Release neurotransmitters to communicate with the next neuron.

Neural Communication

• Electrochemical transmission: electrical impulses trigger the release of chemical neurotransmitters.

Lock-and-Key Process

• Neurotransmitters bind to specific receptor sites.

Glutamate

• Primary excitatory neurotransmitter.
• Makes the postsynaptic neuron more likely to fire.
• Activates memory and learning.

GABA

• Primary inhibitory neurotransmitter.
• Makes postsynaptic neurons less likely to fire.
• Associated with calming feelings of anxiety, stress, and fear.
• Without GABA, postsynaptic neuron activation might cause seizures.

Neuromodulators

• Chemicals that influence multiple neurons over a wider area and for a longer duration.

Dopamine

• Neuromodulator involved in drive, motivation, and motor movement.
• Can have excitatory or inhibitory effects depending on receptor sites in the brain.
• Released when a person is rewarded, reinforcing behaviors linked to pleasure.

Serotonin

• Neuromodulator primarily responsible for regulating mood and the sleep/wake cycle.
• Has inhibitory effects on the postsynaptic neuron.
• Influences appetite, digestion, arousal, and other brain functions.

Neuroplasticity

• The brain's ability to change its structure and function in response to experience.

Adaptive Plasticity

• Occurs after injury to compensate for damage.

Developmental Plasticity

• Occurs naturally during growth.

Synaptic Plasticity

• The ability of synaptic connections to change over time in response to activity or experience.
• These changes include the formation, strengthening, or weakening of synaptic connections.
• Experiences modify neural synapses, causing them to physically change.

Long-Term Potentiation (LTP)

• Long-lasting strengthening of neural pathways due to repeated stimulation of postsynaptic neurons.

Long-Term Depression (LTD)

• Long-lasting weakening of neural pathways due to lack of repeated stimulation of postsynaptic neurons.

Sprouting

• Forming new neural connections.

Rerouting

• Creating alternative pathways for neural signals.

Pruning

• Eliminating unused neural connections to strengthen important ones.

Sympathetic Responses

• Heart rate increases to increase blood flow.
• Adrenal glands secrete stress hormones like adrenaline.

Parasympathetic Responses

• The bladder constricts, and urination is controlled.
• Pupils constrict.

Stress

• A psychological and physiological response to an internal or external stimulus (stressor).
• Demands attention and efforts to cope.

Acute Stress

• Intense psychological and physiological symptoms of brief duration.

Flight-Fight-Freeze Response

• Involuntary and automatic response to a threat.
• Takes the form of escaping, confronting, or freezing.

Chronic Stress

• Endures for several months or longer.

Cortisol

• A hormone released to aid the body in initiating and maintaining heightened arousal during stress.