Human Responses Vocabulary

Neuron (Nerve Cell)

The basic structural and functional unit of the nervous system. Specialised to transmit electrical impulses.

Electrical Impulse

A quick, temporary change in the electrical charge along a neuron's membrane that carries information.

Central Nervous System (CNS)

Consists of the Brain and Spinal Cord. It processes information and coordinates responses.

Peripheral Nervous System (PNS)

Consists of all the nerves outside the CNS. It connects the CNS to the limbs and organs.

Sensory Neuron

Transmits impulses from a receptor (sense organ) to the CNS.

Relay Neuron (Interneuron)

Found entirely within the CNS (brain and spinal cord); connects sensory and motor neurons.

Motor Neuron

Transmits impulses from the CNS to an effector (muscle or gland).

Effector

A muscle or gland that carries out the response dictated by the motor neuron.

Receptor

A specialised structure (often a sense organ) that detects a specific stimulus (e.g., light, sound, pressure).

Reflex Arc

The shortest pathway of a nerve impulse from a receptor to an effector during a reflex action: Receptor → Sensory Neuron → Relay Neuron → Motor Neuron → Effector.

Reflex Action

A rapid, involuntary, automatic response to a stimulus, providing a fast defence mechanism

Five senses

Sight (detects light), Hearing (detects sound waves), Touch (detects pressure/temperature), Taste (detects chemicals in solution), smell (detects chemicals in the air).

Synapse

A specialised junction or gap between the axon terminal of one neuron (presynaptic) and the dendrite or cell body of the next neuron (postsynaptic).

Synaptic Gap (Synaptic Cleft)

The tiny space separating the presynaptic and postsynaptic neurons.

Neurotransmitter

A chemical substance released from the presynaptic neuron into the synaptic gap that transmits the impulse to the postsynaptic neuron.

Vesicle

Small, membrane-bound sacs in the presynaptic terminal that store neurotransmitter molecules.

Receptor Protein

Proteins on the membrane of the postsynaptic neuron that are complementary in shape to and bind with specific neurotransmitters.

Unidirectional Flow

The principle that impulses can only travel in one direction across a synapse (from the presynaptic to the postsynaptic neuron).

Homeostasis

The maintenance of a constant internal environment in the body (e.g., temperature, pH, blood glucose) despite external or internal fluctuations.

Negative Feedback

A control system that works to restore a desired set point. The response is always opposite to the change detected, thus restoring balance/equilibrium (e.g., if temperature rises, the body acts to cool it down).

Hormone

A chemical substance produced by an endocrine gland, carried by the blood, which alters the activity of specific target organs.

Nervous Control

Uses electrical impulses in neurons; fast action; short duration of effect.

Hormonal Control

Uses chemical hormones in the blood; slow action; long duration of effect.

Set Point

The ideal, or target, value for a physiological variable maintained by homeostatic control (e.g. 37oC for human body temperature).

Thermoregulation

The homeostatic mechanism that maintains a constant body temperature (37oC). It is important to keep enzymes from denaturing or slowing down.

Hypothalamus

The region in the brain that acts as the body's thermoregulatory centre, monitoring and controlling body temperature.

Vasodilation (Too Hot)

Blood vessels near the skin surface widen (dilate) to increase blood flow, causing heat to be lost by radiation.

Sweating (Too Hot)

Glands release water onto the skin surface; evaporation of this water removes latent heat from the body.

Vasoconstriction (Too Cold)

Blood vessels near the skin surface narrow (constrict) to reduce blood flow, minimising heat loss.

Shivering (Too Cold)

Rapid, involuntary contraction of muscles to generate heat through metabolic activity.

Pancreas

The gland that secretes the hormones Insulin and Glucagon to control blood glucose concentration.

Insulin

A hormone that decreases blood glucose concentration by promoting the uptake of glucose by cells and converting excess glucose into glycogen in the liver.

Glucagon

A hormone that increases blood glucose concentration by stimulating the liver to break down stored glycogen into glucose and release it into the blood.

Adrenaline (Epinephrine)

The 'fight or flight' hormone, secreted by the adrenal glands. It increases heart rate, breathing rate, pupil diameter, and breaks down glycogen in the liver to increase blood glucose concentration (preparing the body for action).

Type 1 Diabetes

A disease where the pancreas produces little or no insulin. Treatment: Insulin injections (or pump) and blood glucose monitoring.

Type 2 Diabetes

A disease where the body does not effectively use the insulin it produces (insulin resistance). Treatment: Diet, exercise, and sometimes medication or insulin.