Understanding Human Interaction, Nerve Cells, and Systems

Posted on Dec 12, 2025 in Medicine

1. Human Interaction and Coordination

Interaction

  • Essential for survival
  • Internal/External Stimuli

Changes in the environment affecting the body

  • Sensory Receptors

Receive stimuli

Some of them are found in sense organs

  • The Nervous System (Neurons)

Information processor

Receives information from sensory receptors and initiates the appropriate response, coordinating and integrating all cell functions

  • Effector Organs

Endocrine System

  • Endocrine Glands
  • Hormones

Musculoskeletal System

  • Muscles and Bones
  • Movement


2. Nerve Cells

Two types of cells

  • Neurons

Highly Specialized

Star-Shaped Cells

Don’t regenerate

  • Dendrites
  • Soma
  • Nerve Fibre
  • Neuroglia

Support, nourish, and protect neurons

  • Astrocytes
  • Oligodendrocytes
  • Schwann Cells


3. Nerve Impulses and Synapses

Synapses: when the nerve impulse passes from one neuron to the next via connections

Three parts

  • Presynaptic Terminal

End of axon of the first neuron

Contains numerous synaptic vesicles that store neurotransmitters

  • Synaptic Cleft

Small space between two neurons

  • Postsynaptic Terminal

Dendrites or soma of the second neuron

Process

  1. The nerve impulse reaches the end of the presynaptic neuron’s axon
  2. The neuron releases the neurotransmitters in the synaptic vesicles into the synaptic cleft
  3. The neurotransmitters cross the synaptic cleft
  4. They join to specific receptors in the membrane of the postsynaptic neuron
  5. This generates a new electric current or nerve impulse in the second neuron
  6. The new impulse passes from the soma to the end of the axon


4. The Nervous System

Coordinates all the body’s functions

Responsible for intellectual function, emotions, and feelings

Divided into two parts

  • Central Nervous System

Responsible for higher cognitive functions, general sensory integration, and coordination

Consists of two parts

  • Grey Matter

Neuron somas and dendrites

  • White Matter

Neuron axons covered in the myelin sheath

Consists of brain and spinal cord, protected by

  • Skull and Spinal Column
  • Meninges

Nerve Cells

  • Sensory Neurons

Carry information from the receptors to the central nervous system

  • Motor Neurons

Carry information from the central nervous system to the effector organs

  • Interneurons

Connect sensory and motor neurons


5. The Endocrine System

Endocrine glands that produce hormones

  • Nerve Information

Transmitted by electrical impulses and chemical messengers

Quick Response

  • Endocrine Information

Transmitted by chemical messengers (travel through the blood to their target cells)

Lower Response

Hypothalamic-Pituitary Axis

  • Regulates function of the endocrine system
  • Regulates the activity of the pituitary gland using hypothalamic releasing hormones
  1. The hypothalamus sends out releasing hormones which stimulate the pituitary gland to secrete/produce pituitary hormones
  2. The pituitary hormones act on their target organs. These organs are endocrine glands that respond by secreting other hormones
  3. When these final hormones are released, blood receptors send messages to the hypothalamus and pituitary gland, preventing the secretion of their respective hormones
  4. This stops the cascade of hormone release

Pituitary Hormones

  • Vasopressin
  • ACTH
  • Oxytocin
  • TSH
  • FSH
  • LH
  • GH
  • LTH

Endocrine Glands

  • Pineal Gland

Regulates sleep cycle

  • Pituitary Gland

Pituitary hormones

  • Parathyroid Glands

Parathyroid hormone

  • Thyroid Gland

Thyroxine – stimulates cell metabolism, growth, and development

Calcitonin – bone calcification by reducing blood calcium levels

  • Pancreas

Insulin – reduces blood glucose levels and stimulates storage of glycogen

Glucagon – increases blood glucose levels

  • Adrenal Glands

Cortex – corticosteroids

Medulla – adrenaline

  • Testicles

Androgens

Testosterone

  • Ovaries

Estrogens

Progesterone


6. Nervous and Endocrine System Health

Drugs

  • Substances that affect the normal activity of the central nervous system
  • Cause different feelings, from relaxation to euphoria

Withdrawal Syndrome

  • Physiological dependence on drugs or alcohol


Brain

  • Cerebral Cortex

Receives, interprets, and processes information from sense organs

Voluntary motor responses

Intellectual and mental functions

Regulates function of the rest of the nervous system

  • Limbic System

Regulates endocrine system

Responsible for emotions, feelings, and basic instincts

  1. Cerebrum
  2. Cerebellum

Motor coordination and balance

Movements precise and coordinated

Makes us aware of our spatial orientation

  1. Brain Stem

Regulates the autonomic functions that keep us alive

(Heartbeat, respiratory movements, blood pressure…)

  1. Hypothalamus

Controls the pituitary gland (regulates the endocrine system and autonomic nervous system)

Regulates hunger, thirst, body temperature, biological rhythms

  1. Epithalamus

Contains the pineal gland

Regulates sleep cycle, menstrual cycle…

  1. Thalamus

Association of pleasure/displeasure

Like/dislike feelings to sensory stimuli


Spinal Cord

  • Connected to the Brain Stem
  • White Matter – Outside
  • Grey Matter – Inside
  1. Sensory Root

Stimuli

  1. Spinal Ganglion

Sensory branch of spinal nerve

  1. Motor Root

Answer

  • Conduit Function

Information from the sense organs

Brain’s responses

  • Reflex Function

Involuntary motor responses

  • Peripheral Nervous System

Connects central nervous system to the peripheral organs, receptors, and effectors

Nerve

  • Axons isolated by their myelin sheath
  • Covered in a layer of connective tissue

Nerve Ganglion

  • Cluster of nerve cell bodies

Two types

  • Cranial Nerves

Emerge from the brain

  • Spinal Nerves

Emerge from the spinal cord

Branch off all over the body

Cranial and spinal can be

  • Sensory

Information from sensory organs

  • Motor

Information to effector organs

  • Mixed

Both types of information

Autonomic Nervous System

  • Parasympathetic Nervous System

Constricts pupils

Stimulates saliva

Slows heartbeat

Constricts airways

  • Sympathetic Nervous System

Dilates pupils

Inhibits saliva

Increases heartbeat

Relaxes airways

Somatic Nervous System

  • Sensory Nerves
  • Motor Nerves
  • Controls Voluntary Acts and Reflexes
  • Voluntary Actions and Reflexes

Voluntary Actions

  • Generated consciously in an area of the cerebral cortex

Reflexes

  • Generated consciously in the spinal cord
  • Rapid response
  • Involve reflex arc

+ Sensory Neuron

In the nerve ganglia

Information from the sensory receptors

+ Interneuron

In the grey matter of the spinal cord

+ Motor Neuron

In the grey matter

Reflex response to effector organ