Human Body Functions and Coordination
Interaction and Stimuli
The interaction function allows us to perceive internal and external changes (stimuli), interpret them, and generate coordinated responses for survival.
Stimuli and Receptors
A stimulus is a physical or chemical change that triggers a response. Specialized cells called receptors perceive stimuli and send information to coordination centers.
Types of Receptors
- Internal receptors: Perceive changes inside the body (e.g., blood sugar levels).
- External/Sensory receptors: Perceive external stimuli.
- Mechanoreceptors: Perceive pressure, vibration, and movement.
- Thermoreceptors: Perceive temperature changes.
- Chemoreceptors: Detect chemical substances.
- Nociceptors: Perceive pain.
- Photoreceptors: Sensitive to light.
Coordination Systems
The Nervous System
The nervous system analyzes stimuli, generates orders, and sends them to effectors via nerve impulses. These impulses are transmitted by specialized cells called neurons. The nervous system coordinates fast, short-lived responses like muscle contraction.
The Endocrine System
The endocrine system consists of endocrine glands that release hormones into the bloodstream. Hormones coordinate internal organs by triggering chemical reactions, resulting in slower, longer-lasting responses.
Responses and Effectors
Effectors execute the body’s responses. These include muscles (contract) and endocrine glands (secrete substances).
Sensory Perception
Smell
Olfactory cells (chemoreceptors) detect volatile substances. These substances enter the nasal passages, dissolve in mucus secreted by glands in the olfactory mucosa, and stimulate olfactory cells. Nerve impulses are then sent to the brain via the olfactory nerve.
Touch
Thermoreceptors (heat/cold), mechanoreceptors (contact/pressure), and nociceptors (pain) contribute to our sense of touch. Receptors in the skin send impulses to the brain via different nerves.
Taste
Gustatory cells (chemoreceptors) detect chemical substances in food dissolved in saliva. Located within taste buds, these cells send impulses to the brain via the gustatory nerve.
Hearing and Balance
Mechanoreceptors in the ears are responsible for hearing and balance. Auditory cells detect vibrations, while balance cells detect movement. Sound waves vibrate the eardrum, transmitting vibrations through the ossicles to the cochlea. This stimulates auditory cells, sending impulses via the auditory/cochlear nerve. Balance cells in the semicircular canals and cavities send impulses via the vestibular nerve.
Sight
Photoreceptors in the eyes detect light variations. Light enters the cornea, passes through the pupil (which adjusts to light intensity), and is focused by the lens onto the retina. Photoreceptor cells send impulses via the optic nerve.
Nervous Coordination
Nerve Impulses and Synapses
Nerve impulses are electrical signals transmitted along neuron membranes. The transmitter neuron sends the message, and the receptor neuron receives it. Neurotransmitters, stored in axon terminals, transmit messages across synapses.
Nerve Impulse Transmission
- Impulse reaches the axon terminal.
- Neurotransmitters are released into the synaptic cleft.
- Neurotransmitters bind to the receptor neuron, generating a new impulse.
- The new impulse is transmitted.
The Nervous System Structure
The nervous system receives, processes, and coordinates information, generating orders for effectors.
Encephalon
Protected by the skull and meninges, the encephalon contains cerebrospinal fluid.
- Brain: Divided into the cerebral cortex (responsible for awareness, advanced functions, and memory).
- Cerebellum: Controls balance and voluntary movements.
- Brainstem: Connects the encephalon to the spinal cord and controls involuntary functions.
Spinal Cord
Protected by the spine, the spinal cord connects the encephalon to the body, transmitting impulses and coordinating reflex actions.
Peripheral Nervous System (PNS)
The PNS connects the CNS to organs. It comprises 31 pairs of spinal nerves and 12 cranial nerves, divided into sensory and motor nerves. The PNS is further divided into:
- Somatic PNS: Controls voluntary movements.
- Autonomic PNS: Controls involuntary movements. It is divided into the sympathetic nervous system (stress response) and the parasympathetic nervous system (relaxation).
Nervous System Function
Reflex Actions
Reflex actions are fast, involuntary responses controlled by the spinal cord. The reflex arc involves:
- Receptor: Perceives the stimulus.
- Sensory nerve: Transmits the impulse.
- Interneuron: Generates a response.
- Motor nerve: Transmits the order.
- Effector: Executes the response.
Voluntary Actions
Voluntary actions are conscious responses coordinated by the encephalon.
- Receptor: Perceives the stimulus.
- Sensory nerve: Transmits the impulse.
- Cerebral cortex: Generates a response.
- Motor nerve: Transmits the order.
- Effector: Executes the response.
Endocrine Coordination
- Hypothalamus regulates the pituitary gland: Reacts to stimuli and hormone levels.
- Pituitary gland regulates other glands: Manufactures hormones.
- Hormones regulate organ activity: Distributed through the bloodstream.
- Hormones halt pituitary secretion: Feedback loop.
Sense Organ Health
Vision-Related Diseases
- Blindness
- Conjunctivitis
- Cataracts
- Color blindness
- Refractive anomalies (short-sightedness, long-sightedness, astigmatism)
Hearing and Balance Disorders
- Hearing loss
- Vertigo
Prevention
- Regular eye checkups, Vitamin A
- Avoid noisy environments, use ear protection
Nervous System Health
Disorders
- Psychological disorders (stress, depression)
- Degenerative diseases (Alzheimer’s)
- Brain/spinal trauma
- Addictions
Endocrine System Health
Diseases
- Diabetes
- Hypothyroidism
- Hyperthyroidism
Prevention
- Healthy diet, exercise, avoid alcohol
Locomotor System Health
Bone Problems
- Trauma (fractures)
- Joint dislocations
- Scoliosis
- Osteoporosis
Joint Problems
- Arthritis
- Osteoarthritis
- Gout
Soft Tissue Problems
- Strains
- Sprains
- Muscle contracture