Physio V 1

Central Nervous System

• Motor hierarchy levels are arranged into three. The highest level is responsible for planning and general movement. The middle level splits the general plan into programs and controls the speed and precision of skeletal muscle contractions. The lowest level is the lower motor neurons in the spinal cord which executes the movement.
• Spinal cord consists of white matter and grey matter. White matter is made of nerve fibres that form pathways. Grey matter consists of nerve cell bodies. Afferent nerve fibres bring information into spinal cord. Efferent nerve fibres carry information out of the spinal cord.
• Conductive function of spinal cord relates to the pathways that run up and down the white matter. Ascending pathways carry sensory information to the brain. Descending pathways carry motor commands from the brain to spinal nerves.
• Reflex function relates to reflexes carried out by the spinal cord.
• Reflexes include stretch reflexes, which are triggered by muscle stretch and cause muscle contractions, and other reflexes like flexor reflexes (muscle contraction in response to pain), crossed extensor reflexes (extremity extension to support body) and tonic stretch reflex (contraction caused by gravity).
• Consequences of high spinal cord transection are spinal shock, and the importance of C5. Above C5 transection is typically fatal, whereas below C5 transection may cause spinal shock.
• Damage of pons and medullary damage are often fatal, due to their important role in vital functions like breathing and heart rate regulation. Some of the important reflexes localized in these areas are the breathing reflexes, defense reflexes (coughing, sneezing), vomiting and some sensory reflexes.

Functions of midbrain

• Midbrain is located above the pons. It has a conductive function connecting pathways through the brain and spinal cord, and a reflex function through reflexes.
• Superior colliculi are related to visual system control and eye movements.
• Inferior colliculi are related to hearing function and hearing orientation reflex.
• Periaqueductal grey matter decreases pain perception.
• Locus coeruleus is a region that is related to norepinephrine, and plays a role in alertness and response to stimuli.
• Substantia nigra contains dopaminergic neurons that project to the striatum in the basal ganglia.

Functions of cerebellum

• Controls motor activities before feedback signals which helps predict, control, and coordinate muscle contractions.
• Processes information coming from everywhere to adjust movements and make them precise. It receives information from cerebral cortex, reticular activating system, vestibular receptors, olivary nuclei, hearing and photoreceptors, and spinal cords to understand current position and intended movements.
• Consists of three lobes that work separately and functionally, the flocculonodular lobe, posterior lobe, and anterior lobe.
• Cerebellar cortex is made of granule cells, Purkinje cells, and molecular layers, and all communicate between cells via fibres to determine the way the movement is carried out.
• Deep nuclei of cerebellum transmit information out of the cortex and regulate motor commands to other parts of the body.

Functional parts of cerebellum

• Divided into three lobes - flocculonodular lobe, anterior lobe and posterior lobe, each with unique functions.
• Functional zones are where the flocculonodular lobe functions separately, while the rest of the cerebellum is divided into vermis and hemispheres. Different areas process information related to body parts, with the vermis being especially central.

Functions of thalamus

• Relay center that relays information from other parts of the brain to the cerebral cortex.
• Relays information about sensory input, motor commands, and balance to the cerebral cortex.
• It is also responsible for posture control, emotional regulation, and some aspects of arousal.
• Relay nuclei bring sensory information from the body, hearing, and visual parts, to the cerebral cortex for processing. Association nuclei receive information from subcortical and cortical centers. Nonspecific nuclei regulate the sleep-wake cycle and alertness

Functions of hypothalamus

• Regulates various behavioral programs including thirst, hunger, satiety, sleep, thermoregulation, sexual functions, stress response, and biological rhythms.
• Thirst regulation is triggered by the pre-optic area and paraventricular nuclei which work together.
• Hunger and satiety are regulated by the lateral hypothalamic area (stimulates food intake) and the ventromedial nucleus (decreases food intake).
• Sleep centre works with the suprachiasmatic nuclei, adjusting sleep to the light-dark cycle.
• Thermoregulation involves the anterior and posterior hypothalamus.
• Hypothalamic regulation of sexual functions involves medial and lateral pre-optic nuclei, influencing sexual reproduction and emotions.

Functions of basal ganglia

• Basal ganglia encode the decision to move, regulate the direction and amplitude of movement, and control the expression of emotions and expressions.
• Consist of the caudate nucleus, putamen, and globus pallidus.

Functions of limbic system

• The limbic system is important for regulating emotions, learning, and memory.
• It has various structures including the gyrus fornicatus, hippocampus, amygdala, hypothalamus, and fornix.
• Subcortical centers are located in the hemispheres and hypothalamus regulate emotional reactions and coordinate with autonomic and endocrine effects..
• Hippocampus and Amygdala nuclei play crucial roles in memory related functions by transferring short-term memories to long-term memories.
• Dysfunction within the limbic system may result in the expression of inappropriate behavior and emotional responses.

Speech Mechanism

• Speech is a complex process composed of three parts - phonation, resonance, and articulation.
• Phonation is the production of sound by vibrating vocal cords created by lateral cricoarytenoid muscle function,
• Resonance is the modification of the sound by the upper respiratory tract structures(pharynx, nasal cavity, and oral cavity), affecting the quality and timbre of the sound.
• Articulation involves the movement and coordination of speech muscles in the oral cavity for forming words that are understandable. Broca's area and Wernicke's area work extensively for these tasks.
• Damage to any of these areas can result in aphasia (language impairment).

Circadian Rhythms

• Circadian rhythms are rhythmic changes in physiological parameters within a 24-hour cycle.
• Alertness and temperature typically increase during wake cycles and decrease during sleep.
• Hormone levels also follow circadian patterns, with some peaking during sleep (like growth hormone).

Reticular Activating System

• The reticular activating system (RAS) is a nonspecific system that regulates brain and spinal cord arousal.
• It consists of excitatory and inhibitory parts.
• The excitatory part is mainly located in the midbrain, promoting wakefulness and alertness.
• The inhibitory part mainly resides in the medulla, reducing excitability and slowing down alertness.

Electrical activity of the cerebral cortex

• The electroencephalography (EEG) records the electrical activity in different areas of the cerebral cortex
• During wakefulness, electrical activity shows a synchronized rhythm with high amplitudes and low frequencies. These vary in different parts of the cortex.
• During sleep, electrical waves are characterized as irregular rhythms, with low amplitudes and high frequencies.

Sleep phases

• Sleep consists of several stages, each with distinct EEG patterns, characterized by unique brain wave frequencies and amplitudes.
• NREM (non-rapid eye movement) sleep, comprising Stages 1-4, is associated with decreased physiological arousal and various degrees of relaxation.
• REM (rapid eye movement) sleep (20-25% of sleep) is associated with heightened brain activity, rapid eye movements, and dreaming, along with increased sympathetic activity.

Hormonal control of calcium metabolism

• Calcium is regulated by three hormones - parathyroid hormone, vitamin D3, and calcitonin..
• These hormones work interdependently, maintaining calcium homeostasis in blood.
• Parathyroid hormone increases blood calcium by stimulating bone resorption and promoting kidney calcium reabsorption. Vitamin D3's active form (calcitriol) also enhances intestinal calcium absorption.
• Calcitonin helps lower blood calcium by inhibiting bone resorption and stimulating calcium excretion by the kidneys.

Endocrine function of pancreas

• The pancreas has both exocrine and endocrine functions.
• Islets of Langerhans are composed of four different cell types (α, β, δ, and F cells), each producing specific hormones that regulate blood glucose and other functions.

Insulin secretion

• Insulin secretion is regulated by various factors, including glucose levels in the blood, amino acids and fatty acids, hormones like glucagon and growth hormone.
• Insulin secretion occurs in two phases:
• The acute phase which involves the release of pre-formed insulin from beta cells which has a faster response to the increase of blood glucose level.
• The chronic phase involves the release of insulin that is newly synthesized that is slow and regulated by all the feedback from the body.
• Both phases continue until the blood glucose level falls.
• Insulin regulates carbohydrate, protein, and lipid metabolism in the body.

Consequences of insulin excess

• Hyperinsulinism can cause hypoglycemic coma due to abnormally low blood glucose. This happens because glucose entry into insulin-dependent tissues might be accelerated and the glucose utilization increase, while glucose synthesis is inhibited. The result is that free glucose in the blood decreases and the nerve cells, for example, will have impaired activity.

Sex hormones & regulation of sexual function

• Male sex hormones (primarily testosterone) are produced in the testes and regulate the development of male secondary sex characteristics, muscle mass, and libido.
• Female sex hormones (primarily estrogen and progesterone) are produced in the ovaries and regulate the menstrual cycle, development of female secondary sex characteristics, bone health, and libido.

Hypothalamic connection with neurohypophysis

• Hypothalamic neurosecretory cells in the supraoptic and paraventricular nuclei produce vasopressin (AVP) and oxytocin.
• Vasopressin regulates water balance, and oxytocin influences uterine contractions and milk ejection.

Hormonal regulation of the menstrual cycle

• The menstrual cycle is a cyclic process regulated by anterior pituitary and ovarian hormones (estrogen and progesterone)..

Hormonal regulation after fertilization

• After fertilization, the developing embryo releases human chorionic gonadotrophin (hCG), which stimulates the corpus luteum (a temporary endocrine structure) to continue producing progesterone, preventing menstruation and maintaining a suitable environment for the developing fetus.

Regulation of delivery and lactation

• Labor involves complex interactions between hormones from the fetus, placenta, and mother.
• Oxytocin is critical for uterine contractions, and prostaglandins play a major role in stimulating both uterine contractions and labor itself.

Regulation of sex organ development

• Sex organ development is primarily hormonally driven, beginning with the indifferent gonad in the fetus, which differentiates into either testes or ovaries in response to the presence or absence of certain signals like the Y chromosome and related gene factors..

Regulation of female sexual function

• In women, sexual stimulation can produce a specific response. This is accomplished by the parasympathetic nerves in segments S2-S4 which stimulates vasodilation and erection in the clitoris.
• Other effects of sexual stimuli include increased vaginal gland secretion (lubrication) and contraction of uterine ligaments (increasing vaginal length).

Regulation of male sexual function

• Spermatogenesis, the process of sperm production, is highly dependent on the presence of hormones from the hypothalamus, pituitary.
• Spermatogenesis takes place in the seminiferous tubules of the testes with close interactions between Sertoli cells and germ cells.
• The presence of appropriate levels of spermatogenesis hormones (Follicle stimulating hormone and testosterone), along with other relevant functions like the maturation of sperm in the epididymis are required.