PNS
Acts as a communication network between the CNS and the periphery.
Somatic Nervous System (SNS)
responsible for voluntary control of skeletal muscles and the reception of sensory information from the external environment.
Sensory (Afferent)
Carries info. from receptors in the body to the CNS.
Motor (Efferent)
Sends motor commands from the CNS to muscles.
Autonomic Nervous System (ANS)
Regulates involuntary physiological functions such as heart rate, digestion...
Sympathetic
“fight or flight”
preparing the body for increased energy expenditure.
* Sympathetic nerves arise from the thoracic & lumbar regions of the spinal cord.
Parasympathetic
“rest and digest”
conserving energy & promoting relaxation.
* Parasympathetic nerves arise from the cranial & sacral regions.
- The PNS is composed mainly of spinal nerves, cranial nerves, their ganglia & their ramifications.
Spinal nerves:
- 31 pairs, arise from the spinal cord and are responsible for transmitting signals to and from different regions of the body.
- Each spinal nerve has both sensory & motor fibers.
Cranial nerves:
- 12 pairs, originate from the brain and are involved in sensory & motor functions.
Ontogenesis: the development and growth of an organism from the zygote to its mature form:
Stages of Ontogenesis
- 1. Fertilization:
- The union of a sperm cell and an egg cell to form a zygote.
- Marks the beginning of a new organism’s development.
- 2. Embryonic Development:
- Cleavage: Rapid cell division of the zygote to form a blastocyst.
- Blastulation: Formation of the blastocyst with an outer cell layer (trophoblast) and an inner cell mass.
- Gastrulation: Formation of three primary germ layers (ectoderm, mesoderm, endoderm).
- Organogenesis: Development of organs and tissues from the germ layers.
- 3. Fetal Development:
- Growth and maturation of the developing organism, typically from the end of the embryonic period to birth.
- Organs continue to develop and begin to function.
- 4. Birth:
- The process of being born, marking the transition from prenatal to postnatal life.
- 5. Postnatal Development:
- Growth and maturation after birth, including physical growth, brain development, and the development of motor and cognitive skills.
- This stage includes infancy, childhood, adolescence, and adulthood.
- 6. Aging and Senescence:
The gradual decline in physical and sometimes cognitive abilities.
- The final stage of the life cycle.