Human Nervous System and Sensory Organs Flashcards

Responding to the Environment

• Organisms must respond to their environment for survival.

• Stimuli include light, sound, touch, pressure, taste, temperature, and chemicals.

Coordination Systems

• Advanced animals and humans have two coordination systems:

  • Nervous system: rapid reactions.

  • Endocrine system: slower reactions via hormones.

Human Nervous System

• Two main divisions:

  • Central Nervous System (CNS): brain and spinal cord.

  • Peripheral Nervous System (PNS): 12 pairs of cranial nerves and 31 pairs of spinal nerves.

Receptors and Effectors

• Receptors detect stimuli and send impulses to the CNS for processing.

• Processed information is sent to effectors (nerves or glands).

Nervous Tissue

• Composed of millions of neurons and neuroglia (connective tissue).

• Neurons: structural units of the nervous system.

• Function: conduct nerve impulses.

Neuron Structure

• Myelin sheath: encloses nerve fibers, formed by Schwann cells, and accelerates conduction.

Neuron Classification

• Based on structure (number of extensions) and function (direction of conduction).

• Types include bipolar, unipolar, and multipolar neurons.

Functional Classification of Neurons

• Sensory (afferent) neurons: conduct impulses from receptors to the CNS; mostly unipolar.

• Motor (efferent) neurons: conduct impulses away from the CNS to effectors; mostly multipolar.

• Interneurons: connect sensory and motor neurons in the CNS; multipolar.

Synapse

• Axon of one neuron connects to the dendrite of another without direct contact.

• The gap is called the synapse or synaptic cleft.

Synaptic Transmission

• Synaptic vesicles contain neurotransmitters like acetylcholine or serotonin.

• Neurotransmitter release is one-way, ensuring unidirectional impulse movement.

• Synapses filter unimportant stimuli and prevent CNS overload.

Central Nervous System (CNS) Protection

• Bone (skull and spine), cartilage, and S-shaped curvature.

• Three meninges: pia mater, dura mater, and arachnoid membrane.

• Cerebrospinal fluid.

Cerebrospinal Fluid Functions

• Shock absorption, nutrient supply, waste removal, prevention of dehydration, and maintenance of constant pressure.

Grey Matter vs. White Matter

• Grey matter: neuron cell bodies and dendrites.

• White matter: myelinated axons.

Brain: Cerebrum

• Largest part of the brain with an outer layer called the cerebral cortex.

• Functions include voluntary actions, sensations, and higher mental functions.

Corpus Callosum

• C-shaped structure consisting of white matter (axons) that connects the two hemispheres.

• Functions: conducts impulses between hemispheres, forming a communication bridge.

Cerebellum

• Located behind and below the cerebrum; two hemispheres connected by the vermis.

• Functions: coordinates voluntary actions and controls muscle tone.

Medulla Oblongata

• Extension of the spinal cord with white matter outside and grey matter inside.

• Functions: conducts nerve impulses between the spinal cord and the brain, controls autonomic functions (breathing, heart rate, etc.).

Spinal Cord

• Extends from the medulla oblongata to the lumbar region.

• Dorsal root: sensory neurons with a ganglion (cell body).

• Ventral root: motor neurons.

• Dorsal and ventral roots form the mixed spinal nerve.

• Functions: provides pathways (ascending and descending tracts) and contains reflex centers.

Peripheral Nervous System (PNS) Functions

• Sensory nerves (receptors to CNS) and motor nerves (CNS to effectors).

• Somatic nervous system (voluntary muscles) and autonomic nervous system (involuntary muscles).

Reflex Actions

• Rapid, involuntary response to a stimulus; protective function.

• Reflex centers are mainly in the spinal cord.

• Natural (unconditioned) vs. learned (conditioned) reflexes.

Reflex Arc

• Significance: rapid action to prevent injury and prevents overloading of the brain.

Autonomic Nervous System

• Sympathetic division: prepares the body for emergencies (fight-or-flight).

  • e.g., faster heart rate, higher blood pressure.

• Parasympathetic division: returns the body to normal.

• Two divisions are antagonistic with double innervation of target organs.

Disorders of the Nervous System

• Alzheimer's Disease (AD): irreversible, progressive brain disease.

  • Causes: plaque accumulation, tangled nerves, neurotransmitter deficiency.

  • Symptoms: memory loss, confusion, and mood swings.

  • Treatment: manage symptoms and regulate neurotransmitters.

• Multiple Sclerosis (MS): autoimmune condition affecting the brain and spinal cord.

  • Causes: immune system destroys myelin sheaths.

  • Symptoms: speech loss, inability to walk, and vision problems.

  • Treatment: anti-inflammatory drugs, muscle relaxants, and physical therapy.

Injuries to the Nervous System

• Brain Damage

  • Causes: traumatic brain injury, stroke, hypoxia, cancer, and infection.

  • Symptoms: loss of consciousness, headaches, dizziness, and memory loss.

  • Spinal Damage

  • Causes: trauma, car accidents, violence, sports injuries, and diseases.

  • Symptoms: pain, loss of sensation, breathing difficulties, and muscle spasms.

Effects of Drugs

- Any substance that alters normal body function by stimulating or inhibiting neurotransmitters.
- **Neurotransmitters** - Chemicals released in the synapse to conduct nerve impulses.
 -Addictive drugs increase neurotransmitters and stimulate pleasure centers,  creating the desire for more.

• Three main types of drugs:

  • Stimulants: accelerate nerve impulses (e.g., caffeine, nicotine).

  • Depressants: slow down nerve impulses (e.g., alcohol, heroin).

  • Hallucinogens: cause distorted perceptions (e.g., ecstasy).

• Marijuana / Dagga (Cannabis sativa)

  • It is commonly smoked but can be added to food or infused to drink as a tea.

  • Active ingredient affects brain areas related to memory, concentration, perception and movement.

  • Low-Medium Doses: Drowsiness, reduced coordination, excessive talkativeness, altered sense of time and space.

  • High Doses: Hallucinations, paranoia and panic attacks.

• Heroin

  • Most addictive substance that mimics endorphins causing an exaggerated sense of happiness.

  • Side effects include vision problems, reduced concentration, decreasing libido etc.

  • Sharing needles can increase the odds of diseases like (HIV).

• Ecstasy

  • Stimulant taken in social gatherings dance parties.

  • Side effects includes negative impact on emotions, memory, learning, anxiety, depression.

• Tik / Metamfetamien

  • Creates a feeling of pleasure due to release of neurotransmitter dopamine.

  • Short term symptoms - Enlarged pupils, Assertion, Excessive sweating, Nausea Dizziness, Diarrhoea etc.
    -Long term symptoms - causes insomnia, anxiety, paranoia, hallucinations, violent/aggressive behaviours and eventually death.

Sensory Receptors

• Respond to stimuli: light, sound, temperature, pressure, pain, and chemicals (taste and smell).

Human Eye

• Consists of the following:
  Sclera, Cornea, Choroid, Ciliary Body, Iris, Lens, Retina, Optic Nerve, Vitreous Humor

Pupillary Mechanism

• Reflex reactions adjusting to the amount of incoming light.

• Bright light: pupil constricts, radial muscles relax, and circular muscles contract.

• Dim light: pupil dilates, radial muscles contract, and circular muscles relax.

Accommodation

• Far object (6m or further) Normal Eye

  • Suspensory ligaments exert force on the lens with less convex light is bent less.
    -Near object (Closer than 6m)

  • Siliarily muscles contract with elastic lens becoming more convex, where light rays are refracted more.

Visual Defects

• Short-Sightedness (Myopia) - Nearby objects focus, but far objects can't be seen.
  -Causes by extended eyeball abnormal curvature of the cornea, which can be corrected with concave lenses and surgery.

• Long-Sightedness (Hyperopia) - Distant objects are clearly seen.
  -Causes by a shorter eyeball with abnormal flat cornea, which can be corrected with convex lenses and surgery.

• Astigmatism - Hazy image due to cornea/lens having an irregular shape,which can be treated with medical procedures.

• Cataracts - lens starts getting dense thus not letting enough light passing through, treated with medical procedures.

Human Ear

• Responds to sound stimuli and detects head movements to help maintain balance/equilibrium.

• Human Ear is divided into three parts - External Ear, Middle Ear, and Internal Ear.

External Ear

• Pinna - Captures Sound waves to audience opening

• External Auditory Canal - conducts sound waves

Middle Ear

• Tympanic Membrane - converts sound waves into vibrations

• Middle Ear bones - hammer (Malleus), anvil (Incus) and stapes (Stapes)
  -Oval window - Transmits vibrations from air filled middle ear cavity.

• Round window - pressure waves in the perilymph are absorbed

• Eustachian tube - Connects the Middle ear to the pharynx

Internal Ear

• Vestibular Apparatus - Balance

• Cochlea - Hearing

• Maculae - provides position related info

• Cristae (in Ampulla of semicircular canals) - observes changes

Overall Hearing Mechanism (Summary)

• Amplification due toLever system formed by decrease in size of the ossicles

• Larger tympanic membrane transmitting vibrations to the smaller oval window

Hearing Defects

Conductive deafness - Transferring vibrations to internal part,can be temporary/permanent which could need surgery.
Nerve Deafness - Due to sensory hair-cells getting damaged leading to auditory nerves which can be permanent with/without Cochler implants.