exactly essay 6 - Reflex regulation of the physiological functions. Type of reflexes according to the mechanism of formation and the characteristics of the involved reflex arc. Nerve centre – classification and properties. Brain circulation. Cerebro-spinal fluid (CSF)

sections

what is nerve centre

types of nerve centres

brain circulation

metabolic factors that affect cerebral blood flow

effects of decreased O2

effects of higher pCo2

cerebrospinal fluid

what is nerve centre

A nerve centre is an area, commonly in either a plexus or ganglion that organise a reflex.

Receptor→ nerve centre→ effector

types of nerve centres

1. Respiratory centre- nerve centres in the brainstem controlling aspects of respiration

2. Cardiovascular centre- --accelerator, vasomotor-smooth muscle tone and vessel, cardio- inhibitor- vagus nerve—medulla oblongata

3. Feeding centre- group of cells in the hypothalamus which when stimulated cause hunger.

4. Pontine micturition centre → brain stem → relaxes urethral sphincter → micturition

   Nerve centre can be found in the brain stem and spinal cord segments

brain circulation

• The normal flow of blood within the brain is 50-65 ml of blood/100g of brain tissue/minute.

• Cerebral blood flow is related to the metabolic activity of the tissue.

• Brain requires glucose

concentrations of what affect cerebral blood flow

• Co2 concentration

• H+ ion concentration

• O2 concentration

effects of decreased O2

• Decreased O2 conc. – leads to hypoxia- causes respiratory distress

  • If blood flow becomes insufficient to supply the brain of the needed amount of oxygen

  • oxygen deficiency mechanisms cause vasodilation.

  • Increasing CBF and returning O2 levels to normal.

  • Low levels have proven to cause coma and diminished neural activity.

effects of higher pCo2

• increase in arterial PCo2 increases CBF.

• CO2 combines with water in the body fluids to form carbonic acid, → dissociates to form H+ ions

• The H+ ions are used for vasodialation of cerebral levels

• Vasodilation is needed to remove excess CO2 due to its harmful neural effects.

cerebrospinal fluid

• Clear and colourless fluid

• Produced by choroid plexus –mainly 3rd ventricle

• Choroid plexus produces approx.

• 500 *-ml of CSF per day.

• 100-160ml is present at each time

• Cushions brain from impact and nutritive, shock absorber

• Arachnoid granulations drain CSF

• CSF flows throughout the in the brain ventricles and into spinal cord, clearing the metabolic waste from CNS through the blood-brain barrier.

sections

what is reflex

reflex arc is comprised of

types of reflexes

main types of reflex systems

tendon reflexes

withdrawal reflexes

somato-somatic reflex

somato-visceral reflex

viscero-somatic reflex

viscero-visceral reflex

hyporeflexia

hyperreflexia

areflexia

what is reflex

• A quick unconscious response from internal or external stimulus- protects/adapts body to change taken place

• A reflex arc represents the mechanism of physiological function automatically managed and regulated.

• Starts with stimulation of the sensory neurones.

• This enables the next neurones to pass on the information to the muscles or glands required.

• Some reflexes have a Coordination centre within the brain and spinal cord prior to stimulation of the motor nerve.

• The brain modulates reflexes.

• There are many sensory inputs which use reflex arcs, including- skin receptors, the retina, muscle sphincter etc

reflex arc is comprised of

1. Sensory cells, - receptor

2. Afferent neuron

3. Synapse

4. Nerve centre*

5. Efferent neuron

6. In some cases Neuromuscular junction → muscle

7. Effectors- muscle or gland. – reflex action

types of reflexes

• Unconditioned-innate- protection

• Conditioned - developed from unconditional reflexes

main types of reflex systems

1. Autonomic reflexes:

   • Mainly involve internal organs --smooth muscle cells, cardiac muscle cells

   • inhibit or stimulate the cells and glands.

2. Somatic reflexes:

   • Involved in reflex controls of skeletal muscles- voluntary

tendon reflexes

aim to prevent damage occurring , can cause muscles to relax if sensory neurones detect

withdrawal reflexes

part of the autonomic reflexes. E.g. hot object, quick retraction from hot surface.

somato-somatic reflex

plantar reflex

somato-visceral reflex

oculocardial reflex – if pressure applied on eyes, heart rate decreases

viscero-somatic reflex

abdominal wall rigidity

viscero-visceral reflex

pressor reflex---( reflex that constricts arterioles (small blood vessels) and thereby increases the blood pressure.

hyporeflexia

decreased reflex response

hyperreflexia

– exaggerated reflex response

areflexia

absence of reflexes