Spinal nerves

This posting about spinal nerve is not covered under spm syllabus. But i hope the diagrams below can give you some understanding about spinal nerve.

We hv 31 pairs of spinal nerves.


1 is spinal cord; 2 is ventral root; 3 is dorsal root; 4 is spinal nerve

Functional types of neurons in spinal nerves (& other nerves):

1. somatic afferent - sensory from general cutaneous receptors (in the skin) & proprioceptors (in skeletal muscles, tendons, & joints)
2. somatic efferent - motor to skeletal muscles
3. visceral afferent - sensory from receptors in the viscera (smooth muscle, cardiac muscle, & glands)
4. visceral efferent - motor to smooth muscle, cardiac muscle, & glands
   
   *viscera =internal organs; singular (viscus)

The skeletal muscle tissue

1. In general, there are 3 types of muscle tissues.

• Skeletal muscle: which is striated and voluntary
• Cardiac muscle: which is striated and involuntary
• Smooth muscle: which is non striated and involuntary

2. Skeletal muscle tissue:

• involuntary muscle (can be made contract or relax by conscious control through the nervous system)
  
• striated or striped muscle because of the presence of alternating dark & light bands on the muscle fibre.
  
  The structure of skeletal muscle:
  1. Is made up of a large number of cylindrical cells called muscle fibres or myofibres.
  (myofibre = a muscle cell)
  2. Each myofibre/muscle fibre is covered by a plasma membrane called sarcolemma, has many nuclei, & contains many protein fibres (called myofibrils) which enable the muscle fibre to contract.
  3. Each skeletal tissue consists of bundles of muscle fibres & these bundles are separated by connective tissue (also called epimysium)
  
  
  
  What is myofibrils?
  1.Myofibrils are composed of individual contractile proteins called myofillaments. These myofilaments are generally divided into thick and thin myofilaments.
  2. The thin myofilaments are composed mainly of a protein known as actin. Actin filaments are anchored into the z-line of a sarcomere.
  3. The thick myofilaments are composed mainly of the protein myosin. It is the orderly overlapping of the actin and myosin filaments that give cardiac and skeletal muscle their striated appearance (light and dark bands).
  
• The contraction of skeletal muscle tissue comes from the collective contractions of each single muscle fibre, whose contraction in turn comes from the contractions of the protein fibres (myofibrils).
  
• The contraction of skeletal muscle requires energy (ATP) produced by mitochondria within the muscle fibres. (sarcosome = the mitochondria of muscle cell).

What is cardiac muscle?

• Cardiac muscle cells are not as long as skeletal muscles cells and often are branched cells.
  
• Cardiac muscle cells may be mononucleated or binucleated. In either case the nuclei are located centrally in the cell.
  
• Cardiac muscle is also striated.
  
• In addition cardiac muscle contains intercalated discs.
  

What is smooth muscle?

• Smooth muscle cells are described as spindle shaped. That is they are wide in the middle and narrow to almost a point at both ends.
  
• Smooth muscle cells have a single centrally located nucleus.
  
• Smooth muscle cells do not have visible striations although they do contain the same contractile proteins as skeletal and cardiac muscle, these proteins are just laid out in a different pattern.

Production of Proteins/Enzymes

This is a useful video to bring you through the production of proteins/enzyme.

For SPM level, your notes (form 4 chapter 2 & 4) regarding the production of Extracellular Enzyme are sufficient. Terms such as transcription, translation are not covered under spm syllabus.

Synapse & transmission of information

What is synapse?
- it is the site where 2 neurones, or a neurone & an effector cell communicate.

Nerve impulses must cross the synapse in order to carry NI/information along to another neurone. Chemicals are used by a neurone to trasmit an impulse across a synapse.

How transmission of chemical signals across the synapse? (refer notes pg7, #6, memorise this!)

Transmission of NI across synapse is an active process/transport which requires energy/ATP. therefore, the synaptic knob contains abundant of mitochondria for generation of energy.

*pls note that action potential, calcium, sodium ion channels, endocytosis are not covered under spm syllabus.