Coordination and Control in Humans

Fundamental Definitions

• Stimulus: A change in the internal or external environment of an organism that initiates a response.
• Response: A change in an organism or part of an organism brought about by a stimulus.
• Receptor: Part of the organism that detects a stimulus (e.g., sense organs containing specialized receptor cells).
• Effector: Part of an organism that responds to the stimulus (e.g., muscles and glands).

Comparison of Nervous and Endocrine Systems

• Nervous System:     * Messages carried as electrical impulses along nerves.     * Transmission is rapid.     * Targeted to precise places in the body.     * Immediate and short-lasting effect.
• Endocrine System:     * Messages carried by chemicals (hormones) in the blood.     * Transmission is usually slow.     * Targeted to generalized regions of the body.     * Slow and long-lasting effect.

The Human Nervous System Structure

• Central Nervous System (CNS): Composed of the brain and the spinal cord.
• Peripheral Nervous System (PNS): Composed of cranial and spinal nerves.     * Connects CNS to all parts of the body.     * Divided into autonomic and voluntary (somatic) systems.

Parts and Functions of the Brain

• Cerebrum: Controls conscious thought, problem solving, decision making, emotions, intelligence, memory, and language. Processes external information.
• Cerebellum: Coordinates voluntary actions, balance, posture, and movement.
• Medulla oblongata: Controls automatic involuntary actions ($\text{e.g.}$ heart rate, breathing, blood pressure, and peristalsis).
• Hypothalamus: Regulates body temperature, fluid concentration (via $\text{ADH}$), and reproduction (via $\text{FSH}$ and $\text{LH}$).
• Pituitary gland: Secretes hormones such as $\text{ADH}$, $\text{GH}$, $\text{FSH}$, and $\text{LH}$.

Neurone structure and Types

• Sensory Neurones: Transmit impulses from receptors to the CNS.
• Motor Neurones: Transmit impulses from the CNS to effectors.
• Relay (Intermediate) Neurones: Link sensory and motor neurones within the CNS.
• Properties: Irritability (converting stimulus to electrical impulse) and Conductivity (transmitting impulses).
• Anatomical Parts:     * Dendrites: Fibres carrying impulses toward the cell body.     * Axons: Fibres carrying impulses away from the cell body (one per neurone).     * Myelin sheath: Fatty insulation that protects the fibre and speeds up impulse transmission.     * Nodes of Ranvier: Constrictions in the myelin sheath.

Synapses

• Synapse: Tiny gap between adjacent neurones.
• Transmission: Neurotransmitters are released from vesicles in synaptic knobs into the gap.
• Functions: Ensures impulses travel in one direction and allows neurone interconnection.

Voluntary vs. Involuntary Actions

• Voluntary Actions: Consciously controlled by the Cerebrum; involve thought, are learned, relatively slow, and complex.
• Involuntary Actions: Occur without conscious thought; not learned, rapid, and simple. Includes:     * Actions regulated by the autonomic nervous system (e.g., digestion).     * Reflex actions.

Reflex Actions and the Reflex Arc

• Reflex Action: Rapid, automatic response to a stimulus by a muscle or gland.
• Reflex Arc Sequence:     $\text{stimulus} \rightarrow \text{receptor} \rightarrow \text{sensory neurone} \rightarrow \text{CNS (relay neurone)} \rightarrow \text{motor neurone} \rightarrow \text{effector} \rightarrow \text{response}$
• Spinal Reflexes: Controlled by the spinal cord. Examples include pulling a finger from heat or the knee-jerk reflex.
• Cranial Reflexes: Controlled by the brain. Examples include blinking, pupil dilation/contraction, and coughing.

Questions & Discussion

• 5 What are the functions of the following in a neurone?     * a Dendrites: Carry impulses towards the cell body.     * b Axons: Carry impulses away from the cell body.     * c Myelin sheath: Insulate and protect the nerve fibre and speed up transmission of impulses.