Central Nervous System (CNS)

Central Nervous System (CNS) Overview

• The CNS, along with the endocrine system, regulates the various bodily functions and systems.
• The CNS comprises of the brain, spinal cord, and neural networks
• The nervous system is categorized into three main divisions.

  • The somatic nervous system initiates and coordinates voluntary movements.

  • The autonomic nervous system regulates involuntary functions, including heart rate and digestion.

  • The integrative nervous system handles thinking, learning, language, speaking, and emotions.

Neural Synapses

• A synapse marks the junctional area where a nerve terminal communicates with another cell, facilitating signal transmission.

Electrical synapse characters

• Electrical synapses involve the direct cytoplasmic connection of adjacent cells via gap junctions.
• Gap junctions are clusters of ion channels enabling the movement of ions between cells and free flow of ions.
• Action potential transmission is exemplified by:
  • Smooth muscle fibers in visceral smooth muscle.
  • Cardiac cells within the cardiac muscle.

Chemical Synapse Characteristics

• Neurotransmitters such as acetylcholine and norepinephrine transfer information across the synaptic cleft.

Presynaptic Neuron

• An action potential leads to opening of calcium channels.
• The opening of calcium channels prompts the release of neurotransmitters stored in vesicles and the influx of ions.
• Neurotransmitters diffuse across the synaptic cleft before integrating with postsynaptic receptors.

Postsynaptic Neuron

• Neurotransmitter interaction with receptors to open ion channels results in either excitatory or inhibitory effects.

Excitatory Postsynaptic Potential (EPSP)

• Defined by a partial, localized depolarization of the postsynaptic membrane.
• Depolarization occurs due to the release of an excitatory transmitter.
• Sodium channels open, allowing positive electrical charges to flow into the postsynaptic cell, leading to a rise in internal membrane potential.
• Depressed conduction occurs through chloride or potassium channels, or both.
• Decreased diffusion of negatively charged chloride ions goes into the cell.
• Decreased diffusion of positively charged potassium ions leaves the cell.

Inhibitory Postsynaptic Potential (IPSP)

• Characterized by a partial, localized hyperpolarization of the postsynaptic membrane.
• Hyperpolarization is caused by the release of an inhibitory transmitter.
• Chloride ion channels open, allowing negatively charged chloride ions to diffuse into the neuron, resulting in a negative charge.
• Conductance of potassium ions increases out of the neuron.
• Increased negativity occurs inside the cell, making transmission inhibitory.

Characteristics of Sensory Receptors

• Sensory receptors are specialized structures.
• They exist at the termination sensory (afferent) neurons).
• Each receptor uniquely responds to and produces a special type of sensation.

Types of Sensory Receptors

• Mechanoreceptors: activated by pressure or changes in pressure.

  • Hair cells in the organ of Corti are activated.

  • Pacinian corpuscles are activated.

  • Meissner's corpuscles are activated.

  • Baroreceptors in the carotid sinus and carotid arch are activated.

  • Golgi tendon organs are activated.

• Photoreceptors: rods and cons in retina respond to light.
• Chemoreceptors: olfactory, gustatory, and osmoreceptors are activated by specific chemicals such as PH, O₂, CO₂.
• Thermoreceptors: respond to temperature changes.
• Nociceptors: respond to pressure extremes, temperature, or noxious chemicals.
• Pain receptors: these are free nerve endings.
  • Fast pain is carried by group Αδ fibers.
  • Slow pain is carried by C fibers.
  • Substance P, which can be repressed by opioids, is among the neurotransmitters.

Spinal Sensory Tracts

• Three major spinal sensory pathways lead to the brain:
  • Dorsal Column Tract: Conducts touch and proprioception signals without crossing in the spinal cord.
  • Spinothalamic Tract: Transmits pain and temperature sensations via the lateral tract. crude touch is transported via Ventral spinothalamic tract.
  • Spinocerebellar Tracts: Primarily responsible for proprioception, relaying information from muscles, tendons, and joints to the cerebellum. Functions to maintain posture and coordinate lower limb movements.

Pain Sensation

• Pain is an unpleasant sensation caused by actual or impending tissue damage.
• Protective function to initiating the withdrawal reflex.
• It is widely distributed through the nervous system.
• Responds to mechanical, thermal, and chemical stimuli.
• Requires high threshold of stimulation.
• It is almost a non-adapting sensation
• It is perceived at both cortical and thalamic levels.

Pain Receptor Types

• Mechanosensitive pain receptors: respond to strong mechanical stimulation.
• Thermosensitive pain receptors: activated by extreme temperatures.
  • Below 15 °C.
  • Above 45 °C.
• Chemosensitive pain receptors: activated by chemical substances.
  • P-factor
  • Bradykinin.
  • Lactic acid.
• All pain receptors are naked free nerve endings.

Mechanism of Pain Receptor Stimulation

• Pain receptors stimulated chemically by substances released from damaged tissue
  • Bradykinin.
  • Histamine.
  • Serotonin.
  • K+ ions.
  • Prostaglandin.
  • Proteolytic enzymes.
• These substances also lower the stimulation threshold of other pain receptors.

Pain Types by Origin Site

• Cutaneous: Originates in the skin.
• Deep: Originates in muscles, joints, or ligaments.
• Visceral: Originates in internal organs or abdominal regions.

Cutaneous Pain

• The pain is Arises from the skin
• It occurs due to a noxious stimulus.
• It may manifest as fast, well-localized pricking, or slow, diffuse burning pain.
  • It is not referred to other areas.
• Pain is transmitted by A-delta and C-nerve fibers, respectively.

Deep Pain

• Describes a Slow type of pain originating from muscles, joints, periosteum, and ligaments.
• Symptoms and Characteristics are:
  • Dull aching.
  • Conducted by C nerve fibers.
  • Nausea.
  • Sweating
  • Hypotension.
• Muscular spasm occurs in nearby muscles.
• Pain may be referred to other sites.

Intermittent Claudication

• Ischemic pain is present in the muscle of the lower limb.
• Narrowing of blood vessels occurs in the lower limbs.
  • Vascular inflammation
  • Sever arteriosclerosis
• Accumulation of P-factor occurs during exercise
• Pain and limping occurs during muscle activity.

Visceral Pain

• Originates from thoracic and abdominal contents.

• Receptors are fewer and less sensitive, leading to less localized pain.

• Characteristics are:

  • Diffuse.

  • Colicky.

  • Located not specifically.

• Often referred to somatic structures.

• It is also associated with nausea, sweating, vomiting, and bradycardia as well as somatic reflexes such as muscle rigidity and hyperalgesia.

Referred Pain

• Pain is felt away from its original injury site.
• More frequent with visceral and deep somatic pain.
• Cutaneous pain isn't referred.
• Pain is Referred due to convergence of visceral and somatic sensory neurons on the same spinal pathway.
• Pain examples and their sources:
  • Pain of cholecystitis: tip from right shoulder.
  • Cardiac pain: left shoulder and inner side of the left arm.
  • Renal pain: testicular region.
  • Appendix pain: area around the umbilicus.
  • Gastric pain: abdominal structures above the umbilicus.

Headache

• Pain is referred to the surface of the head from deep head structures.

Extracranial Headache Causes

• Eye diseases like errors of refraction.
• Sinusitis involves inflammation of the sinuses.
• Pain from toothache stems from dental issues.
• Otitis media and externa are ear infections of the middle and outer ear.
• Tension and emotions can trigger headache.
• Muscle spasms of the head and neck.

Intracranial Headache Causes

• Meningeal irritation triggers headache.
• Space occupying lesions such as tumors trigger headache.
• Consitpation triggers headache.
• Meningitis from brain inflmmation triggers headache.
• Alchohol consumption triggers headache.
• A lumbar puncture can inadvertently causes a headache.
• Arterial Distension
• Hypertension.
• Migraine.

Migraine Characteristics

• Is characterized by intense, throbbing pain felt on one side of the head.
• It presents with autonomic conditions and are commonly preceded by an aura.

Neurovascular Theory of Migraine

• Migraine involves abnormal excitation of trigeminal nerve axons.
• Vasoactive neuropeptides, including substance P, are released from the nerve endings.
• sterile inflammation and Vasodilation occur with spread to meninges.

Serotonin Theory of Migraine

• Initial rise in plasma serotonin constricts cerebral blood vessels and decreases blood flow, leading to aura.
• Subsequent serotonin drop dilates arteries, causing headache.

Dopamine Theory of Migraine

• Abnormal dopaminergic stimulation occurs.
• It can induce nausea and vomiting.

Vascular Theory of Migraine

• Tension causes vasoconstriction, leading to brain ischemia, then release of vasodilators.
• Arterial distension and headaches occur.

Somatic Sensations from Head

• Sensations has two pathways to conduct sensations from the head:
• Signals are conducted by spinal cervical nerves 2 and 3 via and the spine’s Lemniscal pathway.
• The trigeminal nerve provides all sensation, from upper, mid, and lower sides of the face.
• The ophthalmic branch transmits signals from upper the face forehead, anterior scalp, cornea, conjunctiva, and nasal mucosa.
• The Maxillary branch transmits signals from the middle face, hard palate, teeth, and gums.
• The mandibular branch transmits signals the lower face, teeth, gums, and tongue anterior.

Trigeminal Nerve Injury

• Trigeminal anesthesia results in numbness.
• A lesion occurs with trigeminal ganglion ipsilaterally.
• A lesion occurs with trigeminal leminscus contralaterally.
• It causes corneal inflammation.
• Sensory fiber loss may occur.

Sensory Disturbances: Syringomyelia

• Slowly progresses and is congenital in the spinal cord.
• An abnormal growth of neuroglial tissue and causes fluid to accumulate.
• The lesion affects C and T segments.
• If the lesion extends up the brain stem then it is called syringobulbia
• Manifestations:
  • Loss of sensations and temperature of crossed sides from lesions of lateral spinothalamic.
  • Fine touch and proprioception are intact.
  • Crude touch decreases from harm to the ventral spinothalamic tract.

Manifestations of syringobulbia

• Disease impacts lower neurons of AHCs
• It causes paralysis of the laternal horn
• it causes unilateral or bilateral syndrome
• Paralysis of descending tracts or limb muscles may occur.
• Paralysis or cranial nerves symptoms may occur

Tabes Dorsalis

• Its is a nervous system disease caused by complication from neurosyphilis, which happens 10 -25 years after initial condition.
• Manifestations:
  • Lightening like pain is experienced in the or girdle in their trunks.
  • Degeneration of the Gracile and Cuneate tracks
  • Sensory ataxia: it happens to incoordiantion volentartary movements from the loss of properioceptive signal.

Early and late signs and symptom of tabes dorsalis

• Early:
  • Sensory ataxia occures due lack of prorioception causes difficualty or abnormaltiy o volenteary movemeant
  • Sharp lightining pain occures
• Late:
  • It is transmitted by thin C fibers to resist with compression and pain
  • Superficial, deep, and visceral relfexes are all lost

Symptoms of Peripheral Neuritis

• Disturbaces of a sensorial natrue
• Paraesthesia: numbness or pain felt in certain area's
• Motor disorders.
• Autonomic disorders.

Cases of perpeheral neuritus

• Metabolic disorders such as diabetes
  • Genetic neuropathy from alcohol.
  • or a vitamin deficiency

Motor functions of the spinal cord

• Mechanoreceptors used in Proprioception:
• Muscle spindles
• Golgi tendon organ
• Kinesoreceptors in joint capsule.

Muscle Spindle function

• Length of muscle is consitant
• The length stimuliates excititation and leads to contration of the muscles.
• The process shortenes muscel and releases and discharges from the release and elgination of muscles.

Golgi tendon organ

• Muscle has a junuction in it so it remains sensative.

Kinesthetic receptors in joint capsule

• Has a joint cap
• Contains free never endings
• Its sensitive to acceleration and deacceleration of joints.

Reflex arc

• Reflux muscle
• Afferent nerve: la senasorty
• Rapid conduction
  • Alpha motors

The Types and functions of stretch reflex

• Dynmaic jerks of the tendon
• Functions of skeletal muscle are the followong:
• Essential to maint posture
• Venois return and a lymo flow
• . Abdominal tone prevnets vistreal ptosis

Eye Characteristics on a deeper scope

• The vision system uses two photoreceptor
• cones for photopic
• rods for photic.

Layer description for Eye

• Outer is where layers cornea and schlerea are placed
• Middle is place for choroid and irirs.
• Inner is the part of the cell known part of the retina to absorb light.
• It also carries optic nerve from ganglion cells

Desctription of the conea

• Connea is trasnparent due to its completley avascular
  • Light entry to the eye
• Protectx the delicatye eye structure
• Functions of the iris:*

1. Regulates light and ultraviolet rays.
2. Aids to form clear retinal

• Basic flavor types:*

4. Bitter (back of tongue)
5. Sour (edges of tongue)
6. Sweet (tip of tongue)
7. Salt (dorsum of tongue anteriorly)