Physiology of the Nervous System

Physiology of the Nervous System

Overview

• The nervous system coordinates and regulates body functions through electrical and chemical signals.
• Composed of the central nervous system (CNS) and peripheral nervous system (PNS).

Central Nervous System (CNS)

• Components: Brain and spinal cord.
• Functions:
  • Integrates sensory information.
  • Controls motor responses.
  • Responsible for higher cognitive functions (thinking, memory, emotion).

Peripheral Nervous System (PNS)

• Components: Somatic nervous system and autonomic nervous system.
• Functions:
  • Connects CNS to limbs and organs.
  • Carries sensory information to the CNS and motor commands from the CNS.

Neurons

• Structure:
  • Dendrites: Receive signals.
  • Cell body: Contains nucleus.
  • Axon: Transmits signals away from the cell body.
• Types:
  • Sensory neurons: Relay sensory information to the CNS.
  • Motor neurons: Convey commands from the CNS to muscles.
  • Interneurons: Connect neurons within the CNS.

Action Potential

• Definition: A temporary reversal of the electrical potential across a neuron's membrane.
• Phases:
  • Depolarization: Sodium channels open, sodium ions rush in.
  • Repolarization: Potassium channels open, potassium ions exit.
  • Hyperpolarization: Membrane potential becomes more negative temporarily.
• Propagation: Action potentials travel along the axon via saltatory conduction in myelinated fibers.

Synaptic Transmission

• Process:
  • Action potential reaches axon terminal.
  • Release of neurotransmitters into synaptic cleft.
  • Bind to receptors on post-synaptic neuron, generating a response.
• Types of Neurotransmitters:
  • Excitatory (e.g., glutamate) and inhibitory (e.g., GABA).

Autonomic Nervous System (ANS)

• Divisions:
  • Sympathetic: Prepares body for 'fight or flight' responses.
  • Parasympathetic: Promotes 'rest and digest' functions.
• Regulation: Controls involuntary functions (heart rate, digestion).

Brain Regions

• Cerebrum: Higher functions (thinking, memory, voluntary movement).
• Cerebellum: Coordination of movement and balance.
• Brainstem: Controls basic life functions (breathing, heart rate).

Neuroplasticity

• Definition: The ability of the nervous system to change and adapt in response to experience.
• Importance: Essential for learning, memory formation, and recovery from injury.

Homeostasis

• Role of the Nervous System: Maintains internal balance by regulating physiological processes through feedback mechanisms.

Key Points

• The nervous system operates via complex networks of neurons and synapses.
• Electrical impulses and chemical signals are fundamental to communication within the nervous system.
• Understanding these processes is crucial for the study of behavior, cognition, and health.

Overview of the Nervous System

• Coordinates body functions via electrical and chemical signals.
• Composed of the central nervous system (CNS) and the peripheral nervous system (PNS).

Central Nervous System (CNS)

• Components: Consists of the brain and spinal cord.
• Functions:
  • Integrates sensory information from the body.
  • Controls motor responses to stimuli.
  • Responsible for higher cognitive functions, including thinking, memory, and emotions.

Peripheral Nervous System (PNS)

• Components: Divided into the somatic and autonomic nervous systems.
• Functions:
  • Connects the CNS to limbs and organs.
  • Transmits sensory information to the CNS and motor commands from the CNS.

Neurons

• Structure:
  • Dendrites: Receive incoming signals.
  • Cell body: Contains the nucleus, processes information.
  • Axon: Transmits signals away from the cell body.
• Types:
  • Sensory neurons: Convey sensory information to the CNS.
  • Motor neurons: Send commands from the CNS to muscles.
  • Interneurons: Facilitate communication within the CNS.

Action Potential

• Definition: A brief reversal of electrical potential across a neuron's membrane.
• Phases:
  • Depolarization: Sodium channels open, allowing sodium ions to enter.
  • Repolarization: Potassium channels open, letting potassium ions exit.
  • Hyperpolarization: Temporary increase in negativity of the membrane potential.
• Propagation: Move along the axon through saltatory conduction, which occurs in myelinated fibers.

Synaptic Transmission

• Process:
  • Action potential reaches the axon terminal and triggers neurotransmitter release.
  • Neurotransmitters cross the synaptic cleft and bind to receptors on the post-synaptic neuron, generating a response.
• Types of Neurotransmitters:
  • Excitatory (e.g., glutamate) facilitate action potential generation.
  • Inhibitory (e.g., GABA) decrease the likelihood of action potentials.

Autonomic Nervous System (ANS)

• Divisions:
  • Sympathetic: Activates 'fight or flight' responses during stress.
  • Parasympathetic: Encourages 'rest and digest' processes.
• Regulation: Governs involuntary functions such as heart rate and digestion.

Brain Regions

• Cerebrum: Manages higher cognitive functions, including voluntary movement and reasoning.
• Cerebellum: Coordinates movement, balance, and posture.
• Brainstem: Regulates essential life functions like breathing and heart rate.

Neuroplasticity

• Definition: Ability of the nervous system to adapt and change in response to experiences.
• Importance: Critical for processes such as learning, memory formation, and recovery from injuries.

Homeostasis

• Role of the Nervous System: Maintains internal balance by regulating physiological processes through feedback mechanisms.

Key Points

• The nervous system relies on intricate networks of neurons and synapses for communication.
• Electrical impulses and chemical signals serve as fundamental mechanisms for nervous system operation.
• Understanding these neural processes is vital for exploring behavior, cognition, and health.

Neuron Structure

• Neurons serve as the basic units of the nervous system.
• The cell body (soma) houses the nucleus and key organelles necessary for neuron function.
• Dendrites are branching structures that receive incoming signals from other neurons.
• The axon is a long projection that transmits electrical signals away from the soma toward other neurons or tissue.
• Myelin sheath is an insulating layer around the axon that enhances the speed of signal transmission.
• Nodes of Ranvier are gaps in the myelin sheath where the regeneration of action potentials occurs.
• Axon terminals release neurotransmitters, facilitating communication with other neurons.

Signal Transmission

• Neurons maintain a resting potential of approximately -70 mV, indicating a negative charge inside relative to the outside.
• Action potential occurs when a neuron depolarizes and reaches a threshold level of -55 mV.
• Following depolarization, Na+ ions rapidly enter the neuron, making the inside more positive.
• Repolarization happens as K+ ions exit the neuron, restoring the negative charge.
• There is a refractory period during which the neuron cannot fire again immediately after an action potential.
• Saltatory conduction refers to the process where action potentials leap between nodes of Ranvier, significantly increasing conduction speed.

Neurotransmitters

• Neurotransmitters are chemical messengers that enable signal transmission across synapses.
• Key neurotransmitters include:
  • Acetylcholine: Essential for muscle activation and memory processes.
  • Dopamine: Linked to pleasure, reward pathways, and motor control functions.
  • Serotonin: Regulates mood, sleep cycles, and appetite.
  • Norepinephrine: Affects attention, response actions, and the state of arousal.
  • GABA: The primary inhibitory neurotransmitter, helping to decrease neuronal excitability.

Central Vs Peripheral Nervous System

• The central nervous system (CNS) consists of the brain and spinal cord and is crucial for processing and integrating sensory information.
• The peripheral nervous system (PNS) includes all neural tissue outside the CNS.
• The PNS is classified into two main divisions:
  • Somatic nervous system: Governs voluntary movements of skeletal muscles.
  • Autonomic nervous system: Regulates involuntary physiological functions, further divided into:
    • Sympathetic nervous system: Prepares body for 'fight or flight' responses.
    • Parasympathetic nervous system: Promotes 'rest and digest' activities.

Functional Organization Of Neural Circuits

• Neural circuits consist of interconnected neurons that process specific types of information.
• Types of neural circuits include:
  • Converging circuits: Multiple inputs converge to produce a single output, useful for integrating sensory information.
  • Diverging circuits: One input spreads to multiple outputs, amplifying signals.
  • Reverberating circuits: Neurons stimulate each other in a loop, engaged in rhythmic activities like breathing.
  • Parallel after-discharge circuits: Input traveling through various pathways leads to a single complex output, enabling sophisticated processing.